The long-term effects of surgery (ventriculomyotomy) and oral propranolol therapy were assessed by echocardiographic recordings in 51 studies conducted on 37 patients with hypertrophic subaortic stenosis. The incidence and severity of echocardiographic findings in 19 patients treated with propranolol and in 18 not so treated showed no significant differences. Likewise these findings were unaltered by administration of propranolol in 12 patients who were studied both while they were on the drug and while they were not. In contrast, of 14 patients studied after surgery, only one had persistently abnormal mitral valve motion, two had inconstant abnormality, and 11 had no abnormality at rest. The echocardiographic findings correlated well with independent postoperative hemodynamic assessment. The echocardiographic studies provide a noninvasive objective method for longitudinal evaluation of patients with hypertrophic subaortic stenosis (HSS).