The assessment of cardiac function and dysfunction has often concentrated on particular but piecemeal aspects of ventricular performance. This leads to diverse and often opposite claims on how to define, evaluate and treat heart failure. This review adopts a more integrative approach of appraising the heart, putting it in the context of its role in the circulation. The emphasis is to find a variable which would evaluate the overall function of the heart. Several objective criteria on how to select such a variable were proposed. It was argued that of all currently available variables, cardiac power output fulfils these requirements best. It has long been recognised that cardiac performance assessed at basal resting states do not reflect how much reserve the cardiac pump possesses. Having a variable which represents overall cardiac function implies that cardiac pumping capability and reserve can now be quantified. Cardiac reserve has been found to be a major determinant of exercise capacity in heart failure, and pumping capability a major determinant of prognosis in patients with severe heart failure. Therapeutic attempts at improving the exercise capacity of heart failure patients should be gauged against their ability to improve cardiac reserve. Inotropic agents that augment myocardial performance but compromise cardiac reserve do not improve exercise capacity. An ideal inotrope is one that is synergistic with the sympathetic system and enhances cardiac performance only during exercise.