Chronic cardiac failure is often associated with sleep respiratory disorders. These abnormalities are often unrecognised and represent a marker of the severity of cardiac failure and carry a poor prognosis. The mechanism of apnoea is either central, resulting in periodic nocturnal Cheyne-Stokes respiration, or peripheral by obstruction of the upper respiratory tract. Both mechanisms may be observed in the same patient. Oxygen desaturation, fragmentation of sleep and inspiratory depression lead to sympathetic activation and an increase in let ventricular afterload which can aggravate the cardiac failure. Treatment by continuous positive pressure with a nasal mask can help some patients. It is therefore important to diagnoses these nocturnal disorders using simplified polysomnographic recordings.