Acute coronary artery disease (CAD) is the leading cause of death in the Federal Republic of Germany. In spite of major advances in means of acute treatment, more than half of the patients die as a direct consequence of the disease; in the majority they die prior to hospitalization. One important reason appears to be the lack of scientific insight into the acute pathophysiologic mechanisms and, therefore, of specific and effective means of prevention. The present article presents a model of the triggering mechanisms of acute CAD based on findings of recent clinical-epidemiologic, pathological, and physiologic studies, and a discussion of its possible clinical significance. In recent studies a marked circadian variation with a morning peak was observed for onset of myocardial infarction, sudden cardiac death, and other cardiovascular diseases. These findings indicate specific endogenous and/or exogenous triggering factors that are particularly likely to occur, or to be effective, during that time of day. The relative risk of myocardial infarction is at least two-fold within the first 2 to 3 h after awakening. Some subgroups of patients, however, demonstrated no such circadian variation. Similarly, certain infarct types and cardiac medication appears to interfere with the circadian pattern. In most cases of acute CAD, the pathological findings demonstrate an intracoronary thrombus formed over a ruptured atherosclerotic plaque. During the time interval following arising, the thrombotic tendency is increased (due to platelet activation, reduced endogenous fibrinolytic activity, and increased coronary tone), as well as the risk of plaque rupture (due to an increase of heart rate and blood pressure).(ABSTRACT TRUNCATED AT 250 WORDS)