Aim. To study the synthesis of nitric oxide II (NO) in patients with acute myocardial infarction (AMI) and patients with postinfarction cardiosclerosis (PICS) with chronic cardiac failure (CCF). Material and methods. The study included 125 patients: 35 patients with Q-wave AMI and 90 PICS patients. AMI patients were examined clinically, device and laboratory tests were made to measure NO metabolites in the urine, plasma, culture medium of peripheral blood mononuclear cells on MI day 1 and 21, iNOS was estimated in mononuclear cells of peripheral blood on MI days 1, 2, 7, 14 and 21. PICS patients examination incorporated assays for NO metabolites in 24-h urine and plasma, in blood lymphocytes on M1 day 1, 14 and 28. 2 days before NO tests, all nutritional nitrates and nitrites were excluded from the diet. Control group consisted of 15 nonsmokers aged 33 to 53 years (mean age 43.7 +/- 9.3 years). The level of NO metabolites in the urine was 49.7 mcM, in plasma - 19.7 mcM, in lymphocyte culture - 28.8 mcM. Results. By urinary nitrites/nitrates all the MI examinees were divided into three subgroups: with low, moderate and high levels content of nitrites and nitrates (subgroups 1, 2 and 3, respectively). The correlation analysis has established significant correlations between NO metabolites in urine and plasma in the first MI hours and the data on the clinical status, device characteristics of myocardial lesion extention and prognosis of the disease. The most severe MI course and PICS was seen in subgroup 1, of moderate severity - in subgroup 3, a favourable course - in subgroup 2. Conclusion. Assay for nitrites and nitrates in the urine and plasma is necessary for selection of pathogenetically validated prescription of nitrates to AMI and PICS patients.