The purpose of this study was to explore the influence of exercise tolerance on quality of life (QOL) among patients with heart failure (HF). A descriptive correlational design was used to guide the study. Forty-nine participants who met the selection criteria were enrolled at a medical center in Taipei. Data were collected by using the Short-Form 36 and treadmill tests including an exercise intensity-increasing test and duration-increasing test. The results revealed the mean scores of QOL in terms of physical functioning and mental functioning were 66.99 and 68.82, respectively. The average peak VO2 (exercise intensity tolerance) was 4.65 mets. The average exercise duration tolerances were 768.55, 1717.04 and 1923.48 s for reaching 50% heart rate reserve (HRR), 90% HRR, and completing the whole test, respectively. Patients whose exercise intensity tolerance was > or = 5 mets or whose exercise duration tolerance was > or = 1800 s had better physical functioning, but a significant difference in mental functioning was not observed between the two groups. The findings of the study support the view that exercise testing is safe, feasible, and effective in evaluating exercise tolerance, and that both exercise duration and exercise intensity tolerance were important factors in determining QOL, particularly in physical functioning, for HF patients.