Evidence from in vivo, in vitro, and genetic studies suggests that the reversal as well as the development of left ventricular hypertrophy do not depend solely on hemodynamic load; other factors are involved. Several humoral agents that may affect mitogenesis of cardiac myocytes and nonmyocitic elements have been identified, including the local renin-angiotensin system, norepinephrine, endothelins, transforming growth factor beta, insulin-like growth factor, bradykinin, prostaglandins, and nitric oxide. Animal studies using various models of left ventricular hypertrophy are beginning to suggest that reversal of hypertrophy may decrease mortality, improve coronary flow reserve, and maintain cardiac performance. Studies in humans are less supportive, and more are needed before it may be concluded that reduction of left ventricular mass decreases the cardiovascular morbidity and mortality associated with cardiac hypertrophy.