Stroke volume

What it is

Stroke volume is the amount of blood ejected from the ventricle with one systolic contraction. A common textbook example is about 70 mL in a 70 kg adult male.^[1]

Why it matters

Stroke volume is the per-beat half of cardiac output. If heart rate stays similar, changing stroke volume changes how much blood the heart delivers per minute.^[2,1]

Root causes of abnormal values

• Core relation: Stroke volume rises when the ventricle fills more, the myocardium contracts harder, or outlet load is lower; it falls when preload is low, contractility is weak, or afterload is high.^[1,3]
  Cardiac preloadVenous returnCirculating blood volumeMyocardial contractilityCardiac afterload
• Filling time: Very fast or disorganized rhythm can reduce ventricular filling time, so each beat may eject less blood even if the heart is beating more often.^[3,4]
  Heart rate and rhythmCardiac preload

What it affects

• It links preload, venous return, circulating blood volume, contractility, afterload, cardiac output, blood pressure, and perfusion.^[1,2]

Interpretation traps

• Stroke volume is not usually known from a pulse or blood-pressure reading alone.^[1]

Related conditions