['To assess safety and feasibility of cardiopulmonary exercise test (CPX) in elderly patients with chronic heart failure (CHF) and left ventricular dysfunction.', 'We analysed 395 cardiopulmonary exercise tests (CPXs) performed in 227 clinically stable patients with CHF [mean age 76 years, males 70%, mean New York Heart Association (NYHA) class 2.2 +/- 0.5] and impaired left ventricular function (mean ejection fraction 43 +/- 12%). Ninety-eight out of 395 CPXs (25%) were performed in patients older than 80 years. A standard bicycle exercise ramp protocol was used, with increments of 10 W/min. An expiratory exchange ratio (RER) >or= 1.05 at the peak of CPX was considered as the index of maximal exercise. Average workload was 65 +/- 23 W. No adverse reactions were observed, although one test was stopped for non-sustained ventricular tachycardia. The main reasons for stopping were exhaustion (50%), dyspnoea (30%), maximal predicted heart rate (17%), orthopaedic problems (2.5%) and significant ST segment depression (0.5%). In the overall cohort, 80% of patients achieved an RER >or= 1.05 and, in 56% of them, the RER was >or= 1.15. The anaerobic threshold (AT) was detectable in 80% of CPXs, and mean oxygen consumption (VO2) at AT was 9 +/- 6 ml/kg per min, whereas mean peak VO2 was 11 +/- 3 ml/kg per min. In the cohort of patients aged > 80 years, 71% reached an RER >or= 1.05 and 47% reached an RER >or= 1.15. In these older patients, AT was detectable in 68% of CPXs performed, and the mean peak VO2 was 10 +/- 3 ml/kg per min.'] Is the cardiopulmonary exercise test safe and reliable in elderly patients with chronic heart failure?