SUMMARY Hypertrophic cardiomyopathy (HCM) or idiopathic hypertrophic subaortic stenosis (IHSS) has been defined as an autosomal dominant myocardial disease characterized by specific physical findings, echocardiographic features, asymmetric septal hypertrophy and disordered myocardial architecture. Echocardiographic and scintiphotographic studies failed to reveal evidence of asymmetric septal hypertrophy in four patients with systolic anterior movement of the mitral valve and the typical auscultatory and HYPERTROPHIC CARDIOMYOPATHY (HCM) or idiopathic hypertrophic subaortic stenosis (IHSS) has been defined by certain physical findings," 2 and characteristic hemodynamic," 2 angiographicl'3 and pathologic abnormalities.1' 2, 4-7 Echocardiography provides a valuable noninvasive means of recognizing HCM and, in many institutions, has replaced catheterization as a means of confirming clinical diagnoses. Major echocardiographic features of HCM include abnormal thickness8" of the interventricular septum which is asymmetrically hypertrophied relative to the left ventricular free wall,9-1" systolic anterior movement of the mitral valve'2, '3 and reduction of systolic septal thickening and amplitude of systolic septal excursion.8 Myocardial imaging with a radioactive tracer, thallium 201,'4 has also demonstrated the presence of disproportionate septal thickness and appears to be an additional noninvasive means of diagnosing HCM, particularly when adequate echocardiographic definition of the interventricular septum is not feasible technically.A unified concept of hypertrophic cardiomyopathy as an autosomal dominant myocardial disease characterized by asymmetric septal hypertrophy and disordered myocardial architecture has been proposed.2'" This paper reports four patients with typical physical findings of HCM and echocardiographic documentation of systolic anterior movement of the mitral valve in whom a combination of echocardiographic and scintiphotographic studies and, in one instance, postmortem examination failed to demonstrate asymmetric septal hypertrophy. Systolic anterior movement of the mitral valve and the auscultatory and peripheral pulse abnormalities characteristic of HCM do not therefore appear to be specific for the autosomal dominant myocardial dis- ease characterized by asymmetric septal hypertrophy and abnormal septal histology. Materials and Methods Echocardiographic StudiesThe echocardiographic examinations were performed with a Smith-Kline Ekoline 20 A Ultrasonoscope using a 0.5 inch diameter, 2.25 MHz transducer focused at 7.5 cm. The echocardiograms were recorded on a Cambridge strip chart recorder or Honeywell direct writing recorder (patient 3). Standard techniques were employed to record tracings from the anterior and posterior mitral leaflets and from the septum and posterior wall just below the mitral leaflets. Systolic and end-diastolic cavity dimensions and septal and posterior wall thicknesses were measured at this level,"5 and the ratio of end-diastolic septal to posterior wall thickness calc...

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