An item or power-up that permanently increases one's Life Meter, and particularly common in Action Games and Adventure Games that don't involve (HP-boosting) RPG Elements. After all, if you want more Hit Points, an RPG hero can simply do some Level Grinding, but outside that genre? You'll need one of these babies to do it for you.
Heart Containers usually come as a reward for doing something "big," like defeating a boss or completing a big ol' sidequest. On the other hand, some are just well hidden in the game world itself, inviting the player to search every nook and cranny for these valuable items. Note that Heart Containers may also be split into pieces, requiring a player to collect a certain number of 'fragments' (e.g. 3 to 5) before gaining the benefit of added HP (the flipside being a much larger number of fragments to find).
In games with icon-shaped Life Meters, it's highly likely that these life-giving MacGuffins will be shaped like their display counterpart (such as, uh, hearts). They often restore health as well, and so can serve as a type of After Boss Recovery or Level Up Fill Up.
Related to the Rare Candy (which is usually an addition to the statistical benefits of level-based progression), and Equipment-Based Progression. Not to be confused with Soul Jar, which can sometimes literally be a heart in a container.
The Trope Namer is the Heart Container, an item from The Legend of Zelda.
Of course, the trope naming and trope making Heart Containers from The Legend of Zelda. Full Heart Containers come as rewards for beating bosses, while later games introduced Pieces of Heart (which make a full container with every 4 pieces found) that can be found as rewards for beating Mini Games and doing Sidequests, as well as exploring the heck out of the environment.
The very first game had 5 full containers in very well hidden areas (one outside, and four being a choice between a container and a red potion... you should take the container). The second game repeated this again with 4. The first game's second quest also featured a few old men that could take one full container away if you couldn't pay their price.
Similiarly, both Phantom Hourglass and Spirit Tracks only have full containers...and some of them aren't even hidden at all, they can be bought at a shop.
A Link to the Past had only one full heart container gained in a way other than beating dungeon bosses. The overworld instead had pieces of heart. This was repeated in The Minish Cap, where bosses give them, as well as one very obscure Sidequest that gave you a full Heart Container instead of the usual partial ones. Likewise, in the Oracle games, a full Container in each can be obtained through a special secret from the other game, and another is granted through the Hero Secret.
Twilight Princess abandoned the traditional 4 pieces in favor of 5 because it ended up having two more dungeons (and thus two more heart containers) than originally planned. Better get hunting.
In Skyward Sword, two Life Medals can enhance Link's life meter by one heart each, but only while they're equipped in the Adventure Pouch. Needless to say, increasing the Pouch's space will greatly help here.
Metroid, which originated the same year as Zelda, had Energy Tanks. And continues to have them to this day. To specify, the first game has 6 (12 in Zero Mission on Easy and Normal), the second has 5, Super and the Metroid Prime trilogy have 14 each, Other M has up to 10 but played the Pieces of Heart aspect straight for another 4, and Fusion has twenty.
Banjo-Kazooie has Empty Honeycombs. In the original, 6 Empty Honeycombs equals one new section for your Life Meter. Also, a special jigsaw puzzle at the very end rewards you with red Honeycombs that effectively double the life meter. In the sequels (Tooie and Grunty's Revenge), an NPC named Honey B. would exchange increasing numbers of Empty Honeycombs (1, 3, 5, 7, 9) for new segments on your Life Meter.
Even though the Castlevania games since Symphony have used EXP, a lot have heart containers—both for life, and the ammo that is known as "hearts." Games that have Magic Points have MP boosters, as well.
The Mega Man X series has Sub-tanks, which are effectively whole spare life meters which can be drained to fill the real one, and Heart Tanks, which add a small boost to your maximum health, and some Cyber-Elves in the Zero series which could increase your maximum health at the cost of your rank. The ZX series adds more standard Heart and weapon energy containers.
There are also E-Tanks in the original Mega Man classic games from 2 on (except 8, where it was replaced with Rush dropping random powerups). While sometimes these are just handed out, other times you need a weapon to access it or do some alternate death course. But then you can just buy them.
There's also the HPMemory in Mega Man Battle Network and Star Force. They are justified in the sense that every NetNavi is like a computer antivirus. So when its memory for storing HP increases...
Also in X5 and X6, you can find injured Maverick Hunters scattered through stages who occasionally have life-ups that will increase your max health, and even parts that can be equipped to act as full energy tanks.
Alundra has crystals as your life force. Huge ones added one more.
The second game has heart rings which grow your HP meter. Then there are orbs that do the same to your EP (magic) meter.
Resident Evil 4 has Yellow Herbs. Because both Leon and Ashley have their respective life meters, both are in need of consuming the medicines of these herbs to have higher chances to survive. The same applies for Ada in Separate Ways. Fortunately for all three characters, the increased life meters carry over for the New Game+.
The first Ratchet & Clank game let you add first one, then three more health ("nanotech") spheres by buying Premium and Ultra Nanotech cans. The second game had an experience-based system for gaining health, but nanotech tubes could be found which would increase your maximum health by one, as well as recharging all your existing health and letting off a lightning zap thing which killed everything in sight. Then, in the third game, the nanotech tubes were abandoned in turn, and the series now uses the experience-based system exclusively.
The Bonk's Adventure series had blue hearts which added an extra hit point each.
In Ninja Gaiden you can increase your life meter by collecting one "Lives of the Thousand Gods" item, or nine "Life of the Gods" jewels.
Assassins Creed I has a version of this, your synchronization bar (health) increases as you progress the game by finishing memory sequences, and also for every 15th side-memory you accomplish.
The 3D Prince of Persia games have special drinking fountains that extend your life bar.
Prince of Persia had giant potion bottles that functioned like this in mostly hidden areas; you could get from 3 hearts to 10 over the course of the game. Interestingly, at one point your Shadow can steal one of these from under your nose. When you merge back with him later, you get an extra life point regardless of whether he's actually stolen this potion. Of course, for a Speed Run you can simply avoid all these potions.
In Prince of Persia 2: The Shadow and the Flame, you can raise your heart level from 3 to 12; there's more than nine potions, but that's the cap. It turns out by the end that you will need most of these, because the spell you require to win the game is Cast from Hit Points. The last level contains a side area where you can tediously grind these in case you missed or accidentally destroyed a few.
Seen in the later Kirby games, and inverted in the earlier ones (some game modes or mechanics would reduce your hit points for an increased difficulty).
Ōkami has solar energy. If you collect 3 sun fragments, it will give you another unit of solar energy. There is a total of 15 sun fragments, so that adds up a total of five units of solar energy. Additionally, you can use praise points to increase your solar energy by 12 units, so the grand total is 3 + 12 + 5 = 20. Ōkamiden averts this trope by not having sun fragments, so the only way to increase energy is by collecting Praise (7 times, for a total of 3 + 7 = 10).
Mystical Ninja 64 Starring Goemon has silver and gold Fortune Dolls (those "lucky cat" statuettes with one paw raised), which function like the Zelda series' Pieces of Heart and Heart Containers, respectively.
In Donkey Kong 64, Candy Kong, along with giving instrument upgrades, occasionally gives your characters extra watermelons to give them more health.
In Donkey Kong Country Returns, you can buy an actual heart-shaped container in Cranky's shop, and assign it to Donkey or Diddy (if the game's being played in co-op mode), or between the two (in single-player). Keep in mind that its effect only lasts until you either quit the level or clear it. A special, expensive Banana Juice protects you with 20 containers, but it only lasts for a limited time, and until you die for the first time.
Devil May Cry basically cloned the Heart Container idea. You'd collect blue orb fragments, and each four you collected extended your health bar. There was the occasional whole orb, but most of those were bought rather than found (except the second, which had full blue orbs lying all over the place). Purple orbs do the same for the Devil Trigger meter, though there are no fragments and they are almost never found during gameplay.
Every game after the first allow buying whole orbs as well as getting fragments from Secret Missions, eventually quadrupling your starting Life Meter.
Similarly, Spiritual SuccessorBayonetta has the Broken Witch Hearts, and you can also buy items that give you a maxed out lifebar for the duration of a single level.
Action-packed multiplayer games like the Quake, Unreal and Halo series also have special items that temporarily boost your various health meters beyond their normal limits. Quake and Halo even go so far as to continually whittle away at any health "over the brim" in order to discourage cowardly playstyles.
In God of War, Kratos can collect Gorgon Eyes to expand his health bar, and Phoenix Feathers to expand his magic bar. The third game also has Minotaur Horns, which extend his special item gauge.
In the Chronicles of Riddick video game, there were two types of medical machines—small ones that restored your health, and larger, single use ones that permanently increased it.
The SNES Zelda/Breakout hybrid Firestriker used these, mostly found after bosses, though a few were found in optional areas. There was one such area right before the final boss that could be repeated indefinitely, allowing the player to max their life meter even if they'd missed an expansion along the way, or had needed to use a continue, which reduced your max health to its initial capacity.
Blood has the literal hearts, ripped from bodies, as the "health packs". Creepy, huh?
Cave Story has Health Capsules. However, most are in plain view and only require some thorough exploring.
Your BP increases by breaking bincho fields and defeating Crest Guardians.
Collecting 3 gold rings in Star Fox 64 increases your life bar... until you lose a life or finish the level. Collecting 3 gold rings with an extended life bar grants an extra life.
The gold ring count only resets to zero each time a third is collected, so if you finish a level with two gold rings, you'll only need one to increase the life bar in the next level. In many levels, it's possible to collect two extra lives by way of gold rings if you started with two.
Although there's nothing to collect, in the original Metal Gear Solid, Snake's LIFE increases every time he defeats a boss...unless you're playing on the hardest difficulty level, in which case it just kind of... sits there. This was removed in the remake and sequels, where you simply start with maximum health.
Your maximum health in the original Metal Gear for the MSX increases when you gain in rank, which increases or decreases depending on how well you play.
In Metal Gear Solid 3, Snake's maximum life will increase by a small amount every time he uses the CURE function to restore red health. So technically, you're "collecting" injuries.
The StarTropics series had this. Your max health, represented by hearts, usually increased automatically after clearing a boss. However, there were a rare few Heart Containers scattered around the game, which you could find fairly easily if you were thorough enough. Additionally, if you had less than the maximum, 22 Hearts, picking up a Vitamin-Z capsule would bring your health to the max, though it would slowly decrease to your maximum over time.
In Bionic Commando, while there weren't "Heart Containers" per se, picking up enough "bullets" that the enemy dropped when killed would increase your Max HP by 1 block, until your health topped out, at which point they would do nothing.
There's also the helmet, the bullet-proof vest and the crucifix. The pendant deflected one bullet and was recharged by dying or completing a level, the helmet deflected 3, and the vest deflected every other bullet (the first one that hit, the 3rd, the 5th, etc.)
Each of the Legacy of Kain games had something like this to extend your health: Blood Omen let you find blood vials that increased your health, and as it turned out, there were more of them than you could actually use. Soul Reaver had special wedge-shaped power ups, and every five would boost your health, while Soul Reaver 2 gave you an upgrade every time you activated a Reaver forge. Blood Omen 2 gave you an upgrade when you drank enough blood.
Cosmos Cosmic Adventure has burgers with the functionality of permanently adding an extra hit-point to your character. There are only two in each of the three episodes, so you'll never have more than five bars of health at any given point in the game. Mind you, those extra hit points come in very useful on the later levels of the episode.
The Dark Cloud games have food items that increase the characters' stats, and are given as rewards for successfully reconstructing towns. Fruits of Eden would increase hit points, and can be used by any character —making the player reach a balance so as to keep all characters strong enough for upcoming challenges— while personalized items, such as Potato Pies or Witch Parfaits in the sequel, would increase other stats.
Wario Land Shake It had heart vessels with this purpose, which you had the chance to buy after each world/boss battle was completed.
The Worms games have health crates which randomly drop between turns; any worm which collects a health crate recovers a fixed amount of HP. This counts as a Heart Container since worms technically do not have maximum HP levels; a worm at full health that collects a + 25 crate will gain the full + 25.
War in Darksiders gains an extra heart container after defeating a boss or collecting four Life Stones.
Almost every level of Super Mario Bros. 2 has two Mushrooms hidden in subspace; these function as Heart Containers, but their effect only lasts till you beat the level. The Updated Re-release adds one more mushroom per level. It also features a challenge mode where some of the mushrooms are replaced by Yoshi eggs which you must carry to the exit without dying.
The big, star-tattooed mushrooms in Super Mario Galaxy and its sequel have the same function. Your life meter is usually 3 points worth, but the mushrooms increase it to 6. Keep in mind that, like their SMB2 counterparts, their effect only last during the current level.
An Untitled Story features hearts, collecting which gives 10HP to your beginning 100.
Ricky Slater from Moon Crystal starts with three of the famous internal organs known as hearts. He can increase the counter to five when finding Heart Containers.
In Jables's Adventure, you start with 5 HP. You can collect up to 10 fruit, each of which increase your maximum HP by 2 points.
There are two of these in each main planet (level) in Jet Force Gemini. Each character (Juno, Vela, Lupus) visits three planets before Mizar's Palace, so each can get 6 extra units (worth 5 HP each).
The first No More Heroes game awards Travis with an actual, Zelda-style Heart Container upon the defeat of a boss. An extra Container is gained when the training with Thunder Ryu is completed. The trope is averted in the sequel, however, so Travis can only make his regular health meter more enduring.
Deadly Towers has literal heart containers. They raise maximum health, but unlike ordinary hearts, they do nothing for current health, which only aggravates the game's Nintendo Hard difficulty.
Terraria plays this utterly straight. Heart Containers are called "Life Crystals," and can only be found underground. Upon smashing them, collecting the crystal and using it, the player gains 1 more Heart (20HP), starting at 5 and maxing out at 20. There are also "Mana Stars", the casting equivalent, which can only be made, and then only from falling stars that can only be found above ground—and at night.
The Super Star Wars series uses health swords that extend your life meter when picked up. Since they can be dropped by enemies at random or found in hidden areas, it's possible to grind for these health extending items and have an extremely long life bar. However, your life meter reverts to its default length after completing a level or losing a life.
In Monkey Hero Big Peaches fully restore your health and and an extra peach to your health bar.
Crystal balls in Little Samson add two units to any character's life bar.
The Binding of Isaac has a few items that do this. Keeping with its abusive parent theme, they are dog food in various containers, labeled Breakfast, Lunch, Dinner, and Dessert.
In The Goonies II, rescuing a fellow Goonie gets you extra energy.
La-Mulana has Life Jewels (Sacred Orbs in the remake) that refill and add to your life bar.
In Arcus Odyssey, power-up gems increase your maximum health when blue. If collected while red, the gems increase attack power instead.
The Super Star Wars series had lightsaber pickups that extended your life meter, allowing you to take more hits. Thanks to the Randomly Drops system, you can get many lightsabers in a row and have your life meter be extremely long. However, the life meter reverts to the default length after losing a life or clearing the level.
In Dragons Lair 3D: Return to the Lair, there are Heart Containers that are scattered all over Mordroc's castle. When they are found, they can extend Dirk's health bar.
Minecraft has the Health Boost effect, which increases your maximum health by 2 hearts per tier level. The effect is only temporary; once the effect wears off, all the extra hearts vanish.
Monster Hunter Tri and its expansions (Portable 3rd and Ultimate) have Nutrients which slightly increase the Life Meter during a quest (and its effects are reverted after the quest is over or the player quits or loses). It's possible to upgrade the Nutrients into Mega Nutrients (which grant a greater meter increase) and then Max Potion (which instantly increases the meter to the fullest extent possible).
In Ittle Dew, Ittle starts out with only one full heart of health (allowing her to take a maximum of four hits before getting knocked out), but can increase the size of her life meter by finding four scraps of paper and drawing a heart on them.