We observed breathing pattern abnormalities and arterial oxygen desaturation in patients with stable congestive heart failure during overnight polysomnography. To determine whether congestive heart failure was the reason for these abnormalities, we then studied six additional patients before and after treatment of heart failure. Breathing was more abnormal (153 +/- 87 episodes/night) during decompensation of heart failure and improved with medical therapy (72 +/- 100 episodes/night) (p less than 0.05). Abnormal breathing patterns resolved in three patients, improved in two, and were unchanged in one patient after therapy. Allographic cardiac transplantation in one patient whose sleep study remained unchanged after medical therapy was associated with resolution of breathing pattern abnormalities and severe desaturation during sleep. Therapy-related improvement in nocturnal respiratory events suggests congestive heart failure is a contributing factor for breathing abnormalities and arterial oxygen desaturation during sleep.