Werner Theodor Otto Forßmann was a physician from Germany who shared the 1956 Nobel Prize in Medicine for developing a procedure that allowed for cardiac catheterization. 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.

https://en.wikipedia.org/wiki/Werner_Forssmann