The percentage of older patients with AMI in the total of patients is predominating and is still increasing differentiatedly. The essential cause of there is an increase in complications and in mortality until the 28th day. In a prospective study over 48 months with n = 390 patients we analyzed the age groups less than 65 years (A) and greater than or equal to 65 years (B) regarding their different rates of complications. For the semiquantitative determination of myocardial infarction sizes we used: -Monitoring of ECG, creatinine kinase (CK), and ejection fraction global (EFg). In group A 81% survived, whereas in group B only 60% survived. The average age of the surviving patients was 56.2 years, that of the deceased 64.4 years. The percentage of surviving patients with transmural AMI was 96% in A and 57% in B. In both A and B. CKmax with p less than 0.01 was to be differentiated between non-transmural and transmural AMI. In the deceased CKmax was 89.7 (A) to 59.3 mumol/lxs (B) (p less than 0.05). The percentage with AMI extension was 4% in A and 43% in B, p less than 0.005. Patients of group B showed a significant difference (p less than 0.001) of EFg for non-transmural AMI 59.1 (36-70)%, transmural AMI 31.5%, and deceased 17.3%. In patients with Re-AMI EFg was generally measured to be less than 45%. Re-AMI could be diagnosed in 13% of A and in 29% of B (p less than 0.001). The ICU stay of the surviving patients of the total number of patients could be reduced by 1.1 days in the period from 1984 through 1987. With group B it could be reduced by 0.8 days. The overall stay in hospital (1984-1987) was 19.6 days (A = 18.3; B = 22.4). AMI extension and the Re-AMI result are the decivise factors to the essential increase in complications and cases of death with AMI at older age. The semiquantitative determination of the myocardial infarction size by monitoring makes up an efficient basis for the early assessment of the residual function of the myocardium and of the risk classification.