Cardiopulmonary exercise testing (CPX) is an integral tool for assessing the clinical status and prognosis of patients with heart failure (HF). The present investigation examined differences in CPX variables and prognosis according to reason for test termination. One hundred eighty-three patients with HF (69% men, 31% women; mean age 53 +/- 13 years, left ventricular ejection fraction at rest 24.3 +/- 9.9%) underwent CPX in which the minute ventilation/carbon dioxide production slope, peak oxygen consumption, and peak respiratory exchange ratio were determined. Subjects were tracked for cardiac-related events for 2 years after CPX. Dyspnea and fatigue (general fatigue/leg fatigue) were the primary reasons for test termination in 79 and 104 patients, respectively. Peak oxygen consumption (15.4 +/- 5.7 vs 17.5 +/- 5.9 ml o(2) . kg(-1) . min(-1)) was significantly lower, whereas minute ventilation/carbon dioxide production slope (38.5 +/- 12.8 vs 33.9 +/- 9.8) was significantly higher in the dyspnea subgroup (p <0.05). There were 41 cardiac-related events during the 2-year tracking period. Patients with dyspnea were at significantly higher risk of adverse events (hazard ratio 2.1, 95% confidence interval 1.1 to 4.0, p = 0.02). In conclusion, these results indicate that patients with HF terminating an exercise test primarily because of dyspnea have an increased incidence of cardiac-related events and poorer CPX markers than those limited by fatigue.