Ejection fraction ($\mathrm{EF}$)

Ejection fraction is the fraction of a ventricle's end-diastolic volume lost from its cavity during ejection:The numerator is volumetric stroke volume; $V_{\mathrm{ES}}$ is end-systolic volume. The chamber must be specified: right ventricular ejection fraction concerns the right ventricle, whereas a calculation for the left ventricle concerns its own pair of volumes.

Time-resolved magnetic resonance imaging can estimate the two volumes from a consistently defined cavity. A primary right-ventricular study used cine images and three-dimensional modelling in 120 subjects.^[ref] The ejection fraction is a derived quantity, not an additional independent volume observation.

An original example illustrates its scale dependence. Volumes of 120 and 60 mL give $\mathrm{EF}=50\%$ and stroke volume 60 mL. Volumes of 240 and 120 mL give the same ejection fraction but twice the stroke volume. Consequently, ejection fraction alone does not determine cardiac output; heart rate and an appropriate forward-flow interpretation are also needed.

Its response to shared measurement errors is instructive. Multiplying both measured volumes by the same positive scale $k$ leaves the ejection fraction unchanged. Adding the same offset $b$ does not:For the 120/60 mL example, $k=1$ and $b=20$ mL change the calculated fraction from $0.5$ to $60/140\approx 0.429$, even though the volume difference remains 60 mL. This is an error-model example, not a universal correction for image segmentation. Likewise, cavity volume loss can include backward flow through a heart valve; the formula alone does not establish net useful delivery.