Heart patients worldwide owe a lot to Dr. Werner Forssmann. In the late 1920s, the medical community knew little about how to treat heart ailments. Instead, most of what we knew about hearts came from studying cadavers.
Forssmann was inspired by a textbook that featured a tube entering the heart of a living horse through a jugular vein, which showed you could have a catheter enter the heart of a living thing without killing it. He wanted to prove it was possible to administer a similar procedure on humans.
In 1929, he put himself under local anesthesia and inserted a catheter into a vein of his arm. Not knowing if the catheter might pierce a vein, he put his life at risk. Forssmann was nevertheless successful; he safely passed the catheter into his heart.