Diastolic dysfunction and diastolic failure of the heart have become widely recognized clinical entities. Whereas most conditions related to diastolic dysfunction and failure are the mere consequence of systolic cardiac failure, there also exists a distinct primary form of diastolic failure (1-4). Primary diastolic failure occurs in a large variety of clinical conditions, for example, coronary artery disease, systemic hypertension, diabetes mellitus, aortic stenosis, hypertrophic cardiomyopathy, infiltrative cardiomyopathies, and endocardial fibroelastosis. The underlying pathologic processes include myocardial ischemia, hypertrophy, and fibrosis, all increasing significantly with age. In clinical cardiology, primary diastolic failure has been commonly defined as a condition with classic findings of congestive heart failure with near-normal rest systolic function but with predominantly diastolic dysfunction (5). Diastolic failure of the left ventricle is an early event that occurs more commonly (30% in some series)--at least in the elderly population (6,7)-than previously thought and is often manifest as pulmonary congestion and dyspnea during exercise, that is, exercise intolerance (8). With respect to left ventricular (LV) diastolic cardiac failure, "exercise intolerance" ought to be interpreted in a strict sense, that is, exercise dyspnea caused by pulmonary congestion; it does not incorporate exercise-induced muscular fatigue or physical exhaustion. The latter symptoms of chronic systolic cardiac failure have been ascribed to impaired skeletal muscle metabolism resulting from deconditioning, cytokine activation, deficient endothelial vasodilator response, and loss of anabolic function (9-11).