The purpose of this study was to characterize the response of the human left ventricle to lower body negative pressure (LBNP) and to delineate the relation between left ventricular function and hemodynamic response. Ventricular function curves relating stroke volume to end-diastolic volum were obtained in 12 normal men. Volume data were derived from echocardiographic measurements of left ventricular end-systolic and end-diastolic diameters at rest and during LBNP at -40 mm Hg. End-diastolic volume decreased by 19% (p less than 0.01) and stroke volume by 22% (p less than 0.05). There were no significant changes in heart rate, arterial blood pressure, or end-systolic volume. Thus, moderate levels of LBNP significantly reduce preload and stroke volume, i.e. produce a Starling effect, without affecting contractile state. The absence of significant changes in heart rate and arterial blood pressure in the presence of a significant reduction in stroke volume is consistent with an increase in systemic peripheral resistance medicated by low-pressure baroreceptors.