Dr. Werner Forssmann, according to The Other Wiki:
"In 1929, while working in Eberswalde, he performed the first human cardiac catheterization. He ignored his department chief and tied his assistant to an operating table. Then, he anesthetized his own lower arm and inserted a cannula into his antecubital vein, threading it 65 cm all the way to his heart. Afterwards, he walked some distance to the X-ray department to photograph the catheter which was now lying in his right auricle."