For almost 40 years, a small but intense group of cardiovascular investigators have evaluated cardiac performance by measuring the mass, velocity, and acceleration of blood ejected from the left ventricle. These studies reveal that energy is transferred from ventricle to blood very early in systole, and that the left ventricle is charac terized as an impulse generator. Recent explosive developments in Doppler echocar diography have allowed study of the energetics of ventricular contraction through noninvasive acceleration, velocity, and volumetric flow measurements. Compared against reference...