1). The MB electrophoretic fraction of the serum CPK is specific in the diagnosis old acute myocardial infarction. 2). It allows us to differentiate ischaemia from myocardial necrosis. 3). The absence of this fraction, when found out during a period of 12 to 24 hours after the start of the angina attack allows us to deny the presence of acute myocardial infarction with a high index of precision. 4). Our results show that the serum sample should be obtained between 12 and 24 hours after starting the clinical case, in order to get a higher sensibility and specificity. 5). The quantification of MB fraction might be useful in the calculation of the amount of cardial muscle destroyed. When calculating the amount of cardial muscle destroyed of 125 cases (12.5%) with positive diagnosis of reinfarction and among the same 125, 12 were found occurring for the third time. Is possible that the real frequency of the iterative infarction is even higher, because many cases were dismissed (27.7%) for lack of electrocardiographic data, clearly pointing to myocardial transmural infarction. 6). Investigations were conduced about the evolutative condition of the danger factors.