At least half of patients with heart failure (HF) suffer from sleep apnea. Growing evidence suggests that there may be a strong pathophysiological link between chronic HF and sleep apnea due to nocturnal oxygen desaturation and sympathetic activation. It seems that sleep apnea contributes to systolic and diastolic HF, reduced left and right ventricular function, and arrhythmia (e.g. atrial fibrillation, bradycardia, or ventricular ectopy). Therefore, treatment of sleep apnea might alleviate cardiac symptoms and improve cardiac function. Nevertheless, the exact role of long-term treatment of sleep apnea in HF patients remains to be elucidated, as important clinical endpoints (e.g mortality) have been assessed in only a few studies. Heart Fail Monit 2008;5(4):106-11.