Abstract: The value of the cardiac power index of a functioning heart is determined noninvasively. The index is the second time derivative of the work performed by the left ventricle of the heart between the onset of systole and a point of maximum left ventricular power. Left ventricular work is the product of left ventricular pressure and left ventricular volume. Left ventricular volume can be measured noninvasively by use of gamma camera technology. Left ventricular pressure can be measured noninvasively at a selected arterial location, such as the brachial artery, displaced in the body form the heart. Cardiac pressure pulses can be measured at the arterial location by use of a Doppler ultrasound sensor and processor with compensation for the time delay in the arrival of the pulses from the heart at that location.