Previously, the classification of MI into transmural and subendocardial types has been based on the presence or absence of abnormal Q waves. The pathologic anatomy of necrosis in MI does not necessarily correspond to these ECG criteria. Thus, it is more appropriate to describe myocardial infarcts as Q wave or non-Q wave infarcts. The importance of this classification is underscored by their clinical and pathologic differences and the tendency for more serious prognosis in the non-Q wave infarcts. It should be noted that in Q wave infarcts the volume of necrosis is usually greater than that in non-Q wave infarcts.