Cournand, a French doctor and medical researcher who became an American cititzen in 1941, shared the Nobel Prize in Physiology and Medicine in 1956 with the German Werner Forssmann and Cournand's American mentor Dickinson Richards. They were awarded the prize for a new, interventionist procedure, cardiac catheterisation, which provided medical researchers with important insights into the conditions inside a working human heart and has since become part of the canon of routine clinical procedures in cardiology.