Studies on the long-term effects of exercise training programs on functional capacity and the quality of life in patients with chronic heart failure (CHF) are sparse. The aim of this study was to evaluate the long-term effects of group-based, high-intensity interval training on functional capacity and the quality of life in 80 patients with stable CHF (mean age 70.1 +/- 7.9 years) in New York Heart Association classes II to IIIB. Patients were randomized to either an exercise group (n = 40) or a control group (n = 40). The mean ejection fractions at baseline were 31 +/- 8% in the exercise group and 31 +/- 1% in the control group. The exercise group exercised twice a week for 4 months in addition to 4 consultations with a CHF nurse. Six-minute walking distance, workload and exercise time on a cycle ergometer test, and the quality of life were measured at baseline and 4 and 12 months after enrollment. After 4 months, functional capacity (6-minute walking distance +58 vs -15 m, p <0.001) and the quality of life (Minnesota Living With Heart Failure Questionnaire score +10 vs -1 point, p <0.005) improved significantly in the exercise group compared with the control group. After 12 months, the improvements were still significant in the exercise group compared with the control group for all parameters (6-minute walking distance +41 vs -20 m, p <0.001; workload +10 vs -1 W, p = 0.001; exercise time +53 vs -6 seconds, p = 0.003; quality of life +10 vs -6 points, p = 0.003). In conclusion, the results support the implementation of a group-based aerobic interval training program to improve long-term effects on functional capacity and the quality of life in patients with CHF.