ABSTRACT: Idiopathic hypertrophic subaortic stenosis (IHSS) occurs more commonly in the elderly than is generally believed, and is often unsuspected. In 26 patients above the age of 60, the diagnosis was recognized in only 7 (27 percent) prior to echocardiography. Symptoms included dyspnea in 17, chest pain in 16, and dizziness or syncope in 8 patients. In 10 patients, establishing the correct diagnosis led to therapy with propranolol, with or without discontinuation of digitalis; in 7 of these, the chest pain was significantly reduced. An accurate diagnosis is particularly important because drugs that are useful in other forms of heart disease may have adverse effects in IHSS. Echocardiography is the diagnostic procedure of choice and is indicated in the presence of an unexplained systolic murmur, especially when it is associated with chest pain, syncope or left ventricular hypertrophy. 1979 The American Geriatrics Society