Expansion
Stroke volume divided by end-diastolic volume, normally over 50 per cent
Expansion
Ejection fraction = stroke volume / end-diastolic volume
Since stroke volume is end-diastolic minus end-systolic volume, a typical ventricle holding 120 ml and ejecting 70 ml has an ejection fraction of about 58 per cent.
Ranges in common use:
- Normal: 50 to 70 per cent
- Mildly reduced: 41 to 49 per cent
- Reduced: 40 per cent or less
Two cautions. Ejection fraction is load dependent: it rises with reduced afterload and falls with increased afterload, independent of any change in contractility. And it describes systolic emptying only, so a patient with a stiff, poorly filling ventricle can have breathlessness, raised filling pressures and a completely normal ejection fraction.