This study describes the operative management and outcome of 28 patients with obstructive hypertrophic cardiomyopathy and hemodynamically significant coronary artery disease. Each patient underwent coronary artery bypass grafting and concomitant left ventricular myotomy-myectomy or mitral valve replacement. The mean age at operation was 59 years (range 42 to 74). Five patients (18%) died as a result of operation, four in the immediate postoperative period and one at 2 months postoperatively. Three patients died after the immediate postoperative period of causes unrelated to the operation. The mean follow-up period for the 20 currently surviving patients was 4.8 years (range 4 months to 10.8 years). Nineteen of these patients have experienced substantial functional improvement; all are currently asymptomatic or only mildly symptomatic. Twenty-one patients underwent cardiac catheterization before and after operation; each experienced relief of left ventricular outflow tract obstruction after operation. Twelve patients had a preoperative outflow gradient greater than or equal to 50 mm Hg (average 86 +/- 7) under basal conditions, which decreased to 3 +/- 1.8 mm Hg postoperatively (p less than 0.001). Nine patients had a severe preoperative gradient only with a provocative maneuver (average 93 +/- 6 mm Hg), which decreased to 24 +/- 8 mm Hg postoperatively (p less than 0.001). Five of the 24 patients undergoing left ventricular myotomy-myectomy incurred an iatrogenic ventricular septal defect. This operative complication occurred primarily in patients with a relatively thin ventricular septum (less than 20 mm) and contributed importantly to postoperative death in two of the patients.(ABSTRACT TRUNCATED AT 250 WORDS)