A standardized method for examining hearts and coronary arteries was applied in a study of sudden deaths in 227 autopsies of New Orleans men aged 25-49 years. Of these autopsies, 102 deaths were due to external violence, 125 were from natural causes and 45 occurred suddenly. Of the sudden natural deaths, 14 (31%) were due to coronary heart disease (CHD), seven (16%) were possibly due to CHD and 24 (53%) were due to other causes without evidence of CHD. Large recent myocardial lesions (greater than or equal to 1 cm) were present in 19 (95%) of 20 CHD deaths and in 16 (18%) of 91 non-CHD deaths. The myocardial lesions in sudden CHD deaths were subendocardial involving preferentially the posterior septum and the apex of the heart. The lesions in non-sudden CHD deaths were transmural involving preferentially the anterior, lateral and posterior left ventricle and the base of the heart. Men who died of CHD had extensive coronary atherosclerosis, while those who died of other causes had minimal coronary atherosclerosis. The large proportion of CHD deaths which occurred suddenly (70%) reaffirms the need for primary prevention and the need for improved predictive factors for early detection of CHD.