stroke volume
Stroke volume is how much blood the heart sends out with each beat — the size of one squirt from the pump. At rest it is roughly 70 milliliters from the left ventricle in a typical adult, about a third of a cup.
Arithmetically, stroke volume is the difference between the blood in the ventricle at the end of filling (end-diastolic volume) and what remains after contraction (end-systolic volume). The ventricle never empties completely, so stroke volume is always less than the volume it held.
Three classic levers set stroke volume: preload (how full the ventricle is), afterload (the resistance it ejects against), and contractility (how hard the muscle squeezes). More preload or contractility raises it; more afterload tends to lower it.
Stroke volume is one of the two numbers that combine to give cardiac output — the other being heart rate. The body can boost output by raising either, which is how the heart meets the rising demands of exercise.
If the left ventricle holds 120 mL at end-diastole and 50 mL at end-systole, its stroke volume is 70 mL for that beat.
Stroke volume is simply the blood ejected: filled volume minus residual volume.
Stroke volume equals end-diastolic volume minus end-systolic volume. Express it as a fraction of end-diastolic volume and you get the ejection fraction.