Three cases are presented showing the disappearance of electrocardiographic (ECG) evidence of old inferior wall myocardial infarction (MI) after aorta-coronary bypass surgery. Evidence is presented to suggest that the loss of Q waves may be the result of reperfusion of the ischemic myocardium (two cases) and the "cancelling effect" of a new perioperative myocardial damage upon the ECG evidence of an old myocardial infarction (one case). Q waves do not always indicate permanent myocardial scar formation; they are sometimes transient and reversible. Review of the literature provides further experimental and clinical evidences to suggest that surgical reperfusion of peri-infarction ischemic myocardium is an explanation for the ECG change. Pre- and postoperative angiographic and ventriculographic correlations are needed to further clarify the mechanism and clinical significance of such cases.