In assessing myocardial contractility one may examine isolated heart muscle, the isolated whole heart in controlled circumstances, or the heart in an intact patient. In each situation a number of different indices of contractility may be recorded, each of which has merit but none of which is perfect. Some reflect events occurring during isometric contraction prior to ejection, such as rate of change in intraventricular pressure, maximum velocity of muscle shortening, and velocity of shortening of contractile elements. Others reflect ejection phenomena such as stroke volume, the Starling curve, and the ejection fraction. None of these indices is entirely independent of preload, afterload, and heart rate, and these factors must be controlled. In the whole heart, especially in a clinical setting, this may be difficult. Many clinical studies of myocardial function fail to recognize the need for controlling these variables and therefore are of limited validity.