Patterns of breathing at night were recorded in 4 patients with heart-failure. 2 had periodic breathing while awake and in 2 it developed after they fell asleep. In all 4 the phase of hyperventilation disturbed sleep. These cases also illustrate other problems caused by periodic respiration in heart-failure, which range from tiredness during the day to an inability to sleep for more than a few minutes. Nocturnal waking in the hyperventilation phase of Cheyne-Stokes breathing should be differentiated from paroxysmal nocturnal dyspnoea caused by episodes of pulmonary oedema at night.