• The risk involved in surgical operations on patients with heart disease was studied in 101 patients undergoing 134 operations, and the results were compared with those from a series of 69 surgical patients free from heart disease. The mean ages of the two groups were 61 and 49 years respectively. The gross mortality rates in the two groups were 7.4% and 1.4%, and the rates of incidence of cardiovascular and respiratory complications were 21.6% and 5.6% respectively. The risk for the cardiac patient was therefore greater, but it was not excessive. Patients having an abnormal electrocardiogram as the only cardiac finding and those having hypertensive heart disease or a combination of hypertensive and arteriosclerotic heart disease had no cardiac deaths and suffered no cardiorespiratory complications, but patients with anginal syndrome had a 7% cardiac death rate and a 35% incidence of cardiorespiratory complications. The history is of prime importance in determining the magnitude of the risk, and careful attention to preoperative care, surgical and anesthetic technique, and postoperative care is needed.