Braunwald was the first woman to perform open heart surgery. She was the first woman surgeon certified by the American Board of Thoracic Surgery, and the first woman elected to the American Association for Thoracic Surgery. In 1960, at the age of 32, she led the operative team at the U.S. National Institutes of Health (NIH) that implanted the first successful artificial mitral human heart valve replacement, which she had designed and fabricated. This paper described the first and second attempts that Braunwald and Morrow made to replace the mitral valve with a prosthesis. The first patient did not survive, but the second patient lived.