Dr. Forsmann pioneered the technique of cardiac catheterization, a process by which a cable is inserted through an artery or vein into the heart. Conventional wisdom was that this would be certainly fatal, and Dr. Forsmann was forbidden from trying the technique by his department head. He decided to try the technique on himself. When his assistant protested, he tied them to a table, in order to prevent an alarm being raised. He then gouged his own arm, placed a urinary catheter (designed for something quite different) into one of the veins he located, pushed it up his arm and into his heart.
To seal the deal, he then walked up a flight of stairs (holding the catheter in place) to the x-ray department, and ordered an x-ray of his chest, to prove the location of the catheter.
He was subsequently fired. And fired again from his next position. Having become disillusioned with cardiology, and having now practiced with the urinary catheter, he changed specialties to urology, and became a country doctor.
He was awarded the Nobel prize in 1956.