It is suggested that an occlusive thrombus in a coronary artery develops at the site of an intimal tear but that in the interval between initiation of the thrombus and occlusion of the artery emboli are likely to be shed continually, causing multiple occlusions of myocardial vessels in the area of supply. Multiple and confluent areas of ischaemia can progress to complete occlusion of the coronary artery, or the intimal tear can regress and heal. Such a pathogenesis could account for the very variable clinical and pathological findings in myocardial infarction and for the apparently paradoxical time-relationship between coronary artery thrombosis and myocardial infarction.