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Skeletal Muscle Pump Function Is Associated With Exercise Capacity in Patients With Heart Failure. BACKGROUND: Skeletal muscle pump function may play a key role in maintaining cardiac output (CO), because of the lack of cardiac contractility reserve during incremental exercise in heart failure (HF) patients. We aimed to investigate the relationship between lower leg pump function and surrogate measures of CO during cardiopulmonary exercise testing (CPX) in HF patients.Methods and Results:Consecutive cardiac patients referred for CPX had their lower leg ejection fraction (LgEF) measured using strain gauge plethysmography as a marker of skeletal muscle pump function. We analyzed 88 patients, including 65 HF patients and 23 control subjects. Unlike the control subjects, LgEF correlated with peak oxygen consumption (V̇O2) and peak oxygen (O2) pulse (peak V̇O2: r=0.280, P=0.024; peak O2 pulse: r=0.540, P<0.001) in HF patients. Significant relationships among LgEF, peak V̇O2, and peak O2 pulse were observed in HF patients with reduced EF (peak V̇O2: r=0.367, P=0.026; peak O2 pulse: r=0.658, P<0.001), whereas LgEF in HF patients with preserved EF showed a weak correlation only with peak O2 pulse (r=0.407, P=0.032). LgEF was selected as an independent determinant of peak V̇O2 (β=0.187, P=0.036) and peak O2 pulse (β=0.520, P<0.001) in HF patients. CONCLUSIONS: Lower leg skeletal muscle function may contribute to exercise capacity through an indirect mechanism on cardiac function in HF.