A physically active man began, at the age of 69 years, to have a series of episodes of severe chest pain. At the age of 71 years an attack of intense and persistent substernal pain, unaffected by medication, caused him to enter a hospital. On the third day the return of pain was accompanied by a decline in blood pressure until neither blood pressure nor radial pulse could be obtained and dyspnea and anuria supervened. At autopsy, eight days after the onset of pain, and three and one-half days after the decline had led to the diagnosis of septal perforation, an irregularly shaped opening, measuring 1.5 cm. in diameter, was found in the interventricular septum, permitting communication between the right and left ventricles.