The subject of myocardial energetics was extensively reviewed by Gibbs (62) for Physiological Reviews in 1978 and by Gibbs and Chapman (68) for Handbook of PhysioZogy in 1979. These reviews emphasized studies of the mechanoenergetic coupling of myocardium based on heat (or enthalpy) measurement. Over the last decade, three major lines of research on cardiac energetics have been preeminent. One major line is the study of the heat-load relation by Gibbs and colleagues (62-70, 72, 73, 76, 77). Another major line is the work of Alpert and colleagues on the economy of force generation of the myocardium (7-11, 89, 100, 102, 144). The third major line is ventricular energetics based on a new measure of the total mechanical energy generation of the ventricle by myself and my colleagues (126,164-166,212,213,217, 218,220-233,242,244,246-248,250). One of the major advantages of this new measure of the total mechanical energy of the ventricle is that it allows myocardial contractile efficiency to be determined directly (233,242), which is not possible with the heat-load relation (62, 68, 70) or economy of force (7-10) methods. Another major advantage of this total mechanical energy concept is that it can be quantified by a specific area in the pressure-volume (PV) diagram that is bounded by the end-systolic and end-diastolic PV relations and the systolic PV trajectory. The PV diagram has many advantages over other methods of ana-lyzing cardiac performance that use such myocardial contractile parameters as force and shortening velocity (119, 122, 186). The new measure of total mechanical energy extends the utility of the PV diagram beyond