Male and female death rates from all the major forms of cardiovascular disease were approximately equal until about 1920. Since that time the male:female ratio in fatal ischemic heart disease (IHD) has risen dramatically, but some closely related diseases such as cerebrovascular disease and uncomplicated angina pectoris have maintained sex ratios close to unity. It is difficult to reconcile this divergent trend in the sex ratio of IHD with a simple stenotic-thrombotic view of myocardial infarction (MI) and it is suggested that the modern epidemic of MI in men may be the result of a disorder of muscle metabolism ("vulnerable myocardium") superimposed on a relatively stable background of stenotic-thrombotic arterial disease. The proposed mechanism would also help to explain the selective action of some modern "coronary risk factors" (such as cigarette smoking and physical inactivity) which increase the risk of MI but have little or no effect on the risk of developing cerebrovascular disease or uncomplicated angina pectoris.