To examine the effects of a 12-week tai chi program on quality of life and exercise capacity in patients with heart failure. Thirty patients with chronic stable heart failure and left ventricular ejection fraction ≤40% (mean [± SD] age, 64 ± 13 years; mean baseline ejection fraction, 23% ± 7%; median New York Heart Association class, 2 [range, 1 to 4]) were randomly assigned to receive usual care (n = 15), which included pharmacologic therapy and dietary and exercise counseling, or 12 weeks of tai chi training (n = 15) in addition to usual care. Tai chi training consisted of a 1-hour class held twice weekly. Primary outcomes included quality of life and exercise capacity. Secondary outcomes included serum B-type natriuretic peptide and plasma catecholamine levels. For 3 control patients with missing data items at 12 weeks, previous values were carried forward. At 12 weeks, patients in the tai chi group showed improved quality-of-life scores (mean between-group difference in change, -25 points, P = 0.001), increased distance walked in 6 minutes (135 meters, P = 0.001), and decreased serum B-type natriuretic peptide levels (-138 pg/mL, P = 0.03) compared with patients in the control group. A trend towards improvement was seen in peak oxygen uptake. No differences were detected in catecholamine levels. Tai chi may be a beneficial adjunctive treatment that enhances quality of life and functional capacity in patients with chronic heart failure who are already receiving standard medical therapy.