BACKGROUND: Waon therapy has beneficial effects on chronic heart failure (CHF), peripheral arterial disease, and other various diseases. This was to assess the safety and effect of Waon therapy by echocardiography for the first time in Korea. METHODS: Ten patients with CHF were enrolled. The patients with a light gown were placed in a sitting-position in an evenly maintained 60degrees C dry sauna system for 15 minutes, and then after leaving the sauna, they underwent bed rest with a blanket to keep them warm for an additional 30 minutes. Waon therapy was performed once a day, 5 days a week. RESULTS: Four of the 5 patients who had been treated for more than 2 weeks as protocol noted improvement of heart failure (HF) symptoms and decrease in left ventricular (LV) volume. There were trends in improvement of LV ejection fraction and parameters of diastolic function after the therapy although statistical significance was lack. No one complained of worsening of HF symptoms. In each session, body weight (61.8+/-10.2 kg vs. 61.6+/-10.3 kg, p=0.008) and blood pressure (systolic, 119+/-28 vs. 111+/-27 mmHg, p=0.005; diastolic, 69+/-12 mmHg vs. 63+/-10 mmHg, p=0.005) were significantly decreased, oral temperature (35.9+/-0.4degrees C vs. 37.0+/-0.9degrees C, p=0.017) was increased by 1.0degrees C at the end of sauna bathing, but the heart rate (71+/-10/min vs. 72+/-8/min, p=0.8) was not changed. CONCLUSION: We have experienced Waon therapy which was safe and well tolerated and some beneficial effects for patients with CHF. Large scale randomized study is needed to apply Waon therapy as a promising therapy in Korean HF patients.