Stroke Volume

Stroke volume is the volume of blood ejected by one ventricle of the heart during a single heartbeat. It is calculated as the difference between end-diastolic volume, the amount of blood in the ventricle before contraction, and end-systolic volume, the amount remaining after contraction. Stroke volume applies to both ventricles, although left ventricular stroke volume is commonly emphasized in cardiovascular physiology .¹

Stroke volume is one of the two variables that determine cardiac output, the volume of blood pumped by a ventricle per minute. Cardiac output equals stroke volume multiplied by heart rate. Stroke volume can change as the cardiovascular system adjusts to factors such as exercise, posture, and changes in circulatory demand .¹

Three major factors influence stroke volume: preload, afterload, and contractility. Preload reflects the degree of ventricular filling and myocardial stretch before contraction. Greater filling can increase stroke volume through the Frank-Starling mechanism. Afterload is the mechanical load opposing ventricular ejection, while contractility describes the myocardium's ability to generate force independent of changes in preload and afterload .¹

Stroke volume should not be confused with ejection fraction. Stroke volume is an absolute volume of blood ejected per beat, whereas ejection fraction is the proportion of end-diastolic volume that is ejected, expressed as a percentage. Two ventricles can therefore have the same ejection fraction while ejecting different stroke volumes if their end-diastolic volumes differ .^1,2