[Characteristics of diurnal rhythm in the development of myocardial infarct: risk in the morning hours].

The onset of precordial pain was assessed in all the patients admitted to the Clinical Hospital "Firule" and the Military Hospital, Split, during a six-year period (1981-1986) with acute myocardial infarction (n = 1304). According to the time of onset, all the subjects were stratified in three-hour intervals. The large majority of initial symptoms was registered between 7 and 10 a.m. (372 or 28.53% of all; chi 2 = 317, P less than 0.001). The results of this and other studies of circadian rhythm in coronary events points out to the high risk of morning hours, suggesting specific preventive measures, including pharmacological and life-style interventions.