OBJECTIVES. To investigate the interrelationship between sleep complaints and cardiac symptoms. DESIGN. An epidemiological survey by means of questionnaire. SETTING. Västerbotten and Norrbotten in northern Sweden. SUBJECTS. All 10,216 members of the Swedish Pensioners' Association (SPF). MAIN OUTCOME MEASURES. Sleep disturbances and cardiac diseases. RESULTS. Of the men who slept well, 3.0% stated they were troubled by both spasmodic chest pain ('angina pectoris') and a sensation of irregular heart beats ('cardiac arrhythmia'), 9.9% had angina pectoris alone, 7.9% suffered from cardiac arrhythmia, and 79.2% had neither of these disorders. Amongst the men who slept poorly, the corresponding frequencies were 7.0%, 8.7%, 12.3% and 72.0% (P