A procedure is described for estimation of aldolase of the type A-a tissue-specific enzyme of myocardium--in blood serum under conditions of myocardial infarction. The rate of the enzymatic reaction was estimated by monitoring production of heptulose-1,7-diphosphate. Erythrose-4-phosphate and dihydroxyacetone phosphate were used as substrates of the reaction. High rates of the reaction product accumulation was observed if the compounds, shifting the reaction K'equi, were not added into the experimental samples. Sensitivity of the test was 3-fold increased due to modifications of the original method. Clinical experience with the test showed that activity of aldolase of the type A was distinctly higher in blood serum of patients with myocardium infarction as compared with the healthy donors or with the patients with ischemic heart disease.