Left ventricular hypertrophy is an important adaptive response to chronic pressure or volume overload of the left ventricle. The different types and the pathophysiologic mechanisms of the development of left ventricular hypertrophy in various disease states are reviewed. Detection of left ventricular hypertrophy may be accomplished by electrocardiography and cardiac angiography. Echocardiography, however, is the most accurate noninvasive method to detect the presence and estimate the severity of increased left ventricular mass. The clinical significance of left ventricular hypertrophy and its prognostic implications in several cardiac diseases associated with hypertrophy are discussed. The critical transition stage from adaptive, compensatory and reversible left ventricular hypertrophy to "pathologic" hypertrophy with impaired left ventricular contractility and irreversible myocardial damage is yet unknown. Recent data are presented that provide evidence of regression of left ventricular hypertrophy after medical treatment of patients with hypertension and after aortic valve replacement in patients with aortic valve disease. The clinical importance of regression of hypertrophy and its effects on long-term prognosis remain to be determined.