The normal human heart in a resting, supine position operates at the peak of the ventricular function curve, suggesting cardiac output is controlled by factors other than ventricular filling pressure.
The Starling relationship in the normal human ventricle may be different than usually portrayed. In normal, resting, supine man the ventricular function curve is at its peak at a left ventricular end-diastolic pressure of approximately 10 mm Hg. Below this point is a strong direct relation between filling pressure and stroke work, while at higher filling pressures, a plateau occurs. Limitation of ventricular response is related to a sharply rising ventricular pressure-volume curve at a normal level of filling pressure. Thus, in the supine position, the normal heart is not on the active portion of the ventricular function curve, but is in a unique position in which cardiac output is probably controlled by factors other than ventricular filling pressure. In ventricular failure, the peak of the ventricular function curve is displaced to a higher level.
Parker et al. (Sun,) studied this question.