In order to test whether sudden coronary death patients had a more "vulnerable" myocardium compared with other patients, morphological lesions of the myocardium and conduction system were examined in a selected autopsy series. Chronic inflammatory microlesions, frequently affecting single muscle fibers, predominated among 47 sudden coronary death cases compared with 34 cases with chronic coronary or noncoronary diseases (P less than 0.001). Nonfibrous lesions of the atrioventricular node and the bundle of His also predominated among the sudden death cases (P less than 0.05). Myocardial infarcts of any age as well as relative heart weight (the ratio: total heart weight/body weight) did not differ in the sudden coronary death and the chronic coronary patients. The chronic inflammatory microlesions and the nonfibrous lesions of the conduction system predominating among the sudden death cases may signify a vulnerable condition of the myocardium in sudden coronary death.