Conclusion: Heart failure is associated with lower exercise VO2/W; however, the patient with heart failure is not efficient, but rather accumulating a large oxygen debt (recovery VO2/W) that is repaid following exercise. In addition, the work VO2/W (including both exercise and recovery) is increased in patients with heart failure in comparison to control subjects, and correlates inversely with the percentage of predicted VO2. The large recovery VO2/W is likely due to impaired oxygen delivery to exercising muscle during exercise. The increase in the work VO2/W is probably due to changes in skeletal muscle fiber type that occur in patients with heart failure (type I to type IIb)
