BackgroundPeak oxygen consumption is reduced in patients with symptomatic congestive heart failure, but functional capacity of patients with asymptomatic left ventricular systolic dysfunction has not been assessed by measurement of peak oxygen consumption attained during graded exercise testing.Methods and ResultsPeak oxygen consumption, that is, aerobic capacity (VO2, mL/kg per minute), was determined during graded treadmill exercise using the modified Naughton protocol in 40 patients with left ventricular systolic dysfunction (mean ejection fraction ranging from 14% to 35%; mean, 29%) who, while not receiving any cardiac medications, were totally asymptomatic, and in 41 age-matched normal subjects. Peak exercise duration and VO2were significantly lower in patients with asymptomatic left ventricular systolic dysfunction than in normal subjects (948 ± 273 versus 1239 ± 372 seconds,P< .001, and 22.1 ± 5.9 versus 29.8 ± 7.7 mL/kg per minute, respectively,P< .001), while asymptomatic patients and normal subjects reached similar respiratory equivalents (1.14 ± 0.11 versus 1.11 ± 0.11 [NS]) and level of perceived exertion, using the modified Borg scale (7.4 ± 2.6 versus 8.1 ± 1.5 [NS]). Heart rate, systemic blood pressure, and oxygen pulse response to peak exercise were significantly lower in asymptomatic patients than in normal subjects.ConclusionsAlthough patients with left ventricular systolic dysfunction can be totally asymptomatic in their daily activities, they have experienced a substantial reduction in peak aerobic capacity when compared with normal subjects of similar age.