Quantitative assessment of cardiac pump performance.

1. A means of quantitating left ventricular performance in the conscious dog is presented. Changes in heart rate, stroke volume and cardiac output during elevation of left atrial pressure by acute volume expansion were measured in the conscious dog. 2. The changes in heart rate and stroke volume could be described by y = ym - (ym-yi)e-kp, where yi and ym are initial and maximum values of the variable and p is the change in mean left atrial pressure. 3. Because cardiac output is a derived variable (stroke volume X heart rate) its response is described by a multiple exponential relationship. 4. For a given initial heart rate and inotropic state, the stroke volume response is determined by the Frank-Starling mechanism and the pressure-volume characteristics of the myocardium.