From 1972 to 1980, 23 patients (Group A) with native valve infective endocarditis underwent surgical intervention, often for multiple indications, during the active stage of the infective process because of progressive class III and IV (New York Heart Association) heart failure (12 patients), persistent severe hypotension (3 patients), uncontrolled infection for over 21 days (11 patients), aortic root abscess (2 patients), and pericarditis (1 patient). Eighty-five patients (Group B) with active native valve endocarditis, matched for severity of illness, were treated medically. Two patients (9%) in Group A and 43 patients (51%) in Group B died during the hospital admission (p less than 0.001). Any difference in long-term cumulative survival rate between the 2 groups was largely due to the beneficial impact of surgical management on the hospital mortality. Of 23 patients in Group A, 11 (48%) had an entirely uncomplicated postoperative course. Long-term mortality rates in those with aortic valve endocarditis treated medically (79%) were significantly higher than in those with mitral valve involvement (47%) (p less than 0.05). Patients with aortic valve involvement treated surgically had a better hospital (p less than 0.005) and long-term (p less than 0.0005) survival rate than those treated medically. Two groups at risk for postoperative complications were identified; 3 of 11 patients (27%) with uncontrolled infection had an early postoperative recurrence, and 4 of 7 patients (57%) with an aortic root abscess had postoperative prosthetic paravalvular regurgitation. Surgery therefore effects a substantial reduction in hospital mortality in patients with complicated active infective endocarditis (9% versus 51%), but patients with preoperative prolonged periods of uncontrolled infection or with aortic root abscess are liable to postoperative complications.