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Reduced vs Preserved Ejection Fraction

The single most important number in heart failure is the ejection fraction. It splits the syndrome into two families — a weak pump and a stiff pump — that look alike but are treated differently.

The fraction that gets squeezed out

The ejection fraction (EF) asks a simple question: of the blood sitting in the left ventricle at the end of filling, what percentage is squeezed out with the next beat? If the chamber holds 120 mL and ejects 70 mL, the EF is about 58 percent. A normal heart ejects roughly 55 to 70 percent — it never empties completely, and it does not need to.

Worked example — ejection fraction

End-diastolic volume (full)  EDV = 120 mL
End-systolic volume (after)  ESV =  50 mL

Stroke volume   SV = EDV - ESV = 120 - 50 = 70 mL
Ejection fraction EF = SV / EDV    = 70 / 120 = 0.58 = 58%

Now a weakened, dilated ventricle:
EDV = 200 mL   ESV = 140 mL
SV = 60 mL     EF = 60 / 200 = 0.30 = 30%   (HFrEF)

Note: stroke volume can look almost normal even as EF
collapses, because the chamber has stretched larger.
EF is the squeezed-out fraction; a dilated ventricle can keep stroke volume up while EF falls.

EF is measured most often by echocardiography, an ultrasound of the heart, reported as the left ventricular ejection fraction on echo. It is the number that sorts patients into two great families of heart failure.

A weak pump vs a stiff pump

HFrEF — heart failure with reduced ejection fraction (commonly EF of 40 percent or less) — is the weak-pump problem. The muscle squeezes poorly, often after a heart attack or in a dilated cardiomyopathy. The ventricle stretches and thins, EF drops, and forward output suffers. This is the form with the strongest, best-proven drug treatments.

HFpEF — heart failure with preserved ejection fraction (EF of 50 percent or more) — is the stiff-pump problem. The ventricle squeezes fine, so EF looks normal, but it has become thick and stiff and cannot relax to fill properly. This impaired filling is a problem of diastolic function, which is why HFpEF was long called diastolic heart failure. Filling pressure climbs even though EF reads reassuringly normal.

There is also a middle band, EF roughly 41 to 49 percent, sometimes called mildly reduced. The important habit is not to memorize cutoffs but to grasp the two mechanisms — too weak, or too stiff — because they steer everything that follows.