With the technical assistance ofPatricia J. Klunder SUMMARY An accurate echocardiographic (E) method for determination of left ventricular mass (LVM) was derived from systematic analysis of the relationship between the antemortem left ventricular echogram and postmortem anatomic LVM in 34 adults with a wide range of anatomic LVM (101-505 g). No subject had massive myocardial infarction, ventricular aneurysm, severe right ventricular volume overload or hypertrophic cardiomyopathy. The best method for LVM-E identified combined cube function geometry with a modified convention for determination of left ventricular internal dimen-LEFT VENTRICULAR HYPERTROPHY (LVH) plays a central role in chronic adaptation to pressure or volume overload of the systemic circulation. The degree of hypertrophy parallels the severity of overloadt-" and detection of extreme hypertrophy may indicate a poor prognosis.6'" Thus, logically, serial determination of left ventricular muscle mass (LVM) should be an essential element in the study of such disorders. However, assessment of LVH in man has been limited by the lack of an accurate, well-validated, widely applicable and readily repeatable method for quantitating LVM. The biplane angiographic method of Rackley et al. is accurate by comparison with autopsy LVM, but has seen limited use because of its technical complexity and invasive methodology.9' 10 The noninvasive basis and wide applicability of echocardiography make it an appealing method for the systematic serial evaluation of LVH. Several studies have indicated a close statistical relationship between echocardiographic and angiographic estimates of LVM.55 12 However, the reliability of three-dimensional data derivations from M-mode echocardiography has recently been regarded with considerable skepticism.18' 14 Moreover, the critical comparison be-

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For half a century the systolic click and late systolic murmur lay dormant as innocent auscultatory curiosities. The thirteen years since Barlow related these phenomena to mitral leaflet prolapse have witnessed an astonishing information explosion. We have sought to bring together the accumulated data in this review. An Historical Perspective traces the evolution from the now abandoned "pericardial" or "extracardiac" phases, through the leafletchordal phase (redundancy), the myocardial phase (segmental left ventricular contraction abnormalities), to the anular phase (dilatation and faulty systolic contraction). Functional Anatomy is dealt with in terms of pathology, pathophysiology, hemodynamics, angiocardiography, echocardiography, and physical and pharmacological interventions. Clinical Manifestations are concerned with prevalence, natural history, symptoms, physical signs, electrocardiographic abnormalities and roentgen fingings. The four Major Complications- sudden death, infective endocarditis, spontaneous rupture of chordae tendineae, and progressive mitral regurgitation- are examined. Associated Cardiac Diseases, i.e., Marfan's syndrome, ostium secundum atrial septal defect and atherosclerotic coronary artery disease, are discussed, and a section on Treatment deals chiefly with prophylaxis for infective endocarditis and the management of arrhythmias and chest pain. A final section on Evolving Information considers etiologic concepts, the nature of left ventricular contration abnormalities, the cause of chest pain, the relationship to Marfan's syndrome and ostium secundum atrial septal defect, and the effect of aging and sex differences on leaflet chordal redundancy.

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