Systolic pressure-volume area (PVA) as the energy of contraction in Starling's law of the heart.

We have theoretically proposed "systolic pressure-volume area" (PVA) as a measure of total mechanical energy generated by ventricular contraction. We then experimentally showed that PVA closely correlates with left ventricular oxygen consumption (Vo2) regardless of ventricular loading conditions in a stable contractile state. Although Starling's law of the heart has been generally considered to describe the relation between ventricular preload as the input and the "energy of contraction" as the output, the energy of cardiac contraction has been variously identified with cardiac output, external work, contractile element work, tension-time index, etc., by different investigators. However, none of these variables has been unanimously accepted as the total mechanical energy of contraction because they do not consistently correlate with Vo2 which represents the total energy utilization for contraction. Considering the nature of PVA which has been revealed over the last decade, we now confidently propose that PVA is the most likely expression of the total mechanical energy of contraction that has been pursued for many years as the energy of contraction in Starling's law of the heart.