Aim. To study the relationship between comorbidity and acute heart failure (AHF) complicating myocardial infarction (MI). Material and methods . The analysis included 993 patients with MI from the registry of acute coronary syndrome RECORD-3. Killip class II-IV was recorded in every fifth patient (n=205). Hospital mortality was 6,3%. The mean age was 64,3 (63,5-65,0) years (men — 66,1%). All patients were divided into three groups depending on the number of comorbidities (type 2 diabetes, chronic kidney disease, atrial fibrillation, anemia, stroke, hypertension, obesity, peripheral atherosclerosis, thrombocytopenia). The first group included patients with no more than one disease (n=251), the second one — with 2 or 3 diseases (n=480), and the third one — with 4 or more diseases (n=262). Results. AHF detection rate increased in groups with increasing comorbidity: 12,3%, 17,9% and 33,6%, respectively (p<0,0001). Regardless of the initial therapy, in patients of the first group without AHF the hospital mortality rate did not exceed 1%. In patients of the third group with Killip class II-IV AHF the hospital mortality was the highest and also did not depend on the choice of treatment strategy (24,6% with conservative management, 31,6% with percutaneous coronary intervention (PCI)). PCI made it possible to reliably (p<0,05) reduce the risk of hospital mortality in patients of the second and third groups without AHF relative risk 4,3 (1,0-19,9) and 4,2 (1,1-18,3), respectively. Analysis of a 1-year follow-up revealed that AHF is a death predictor after hospital discharge independent of the comorbidity severity: 11,1%, 13,3%, and 14,3%, respectively. In patients without AHF a 1-year mortality increased from the first to the third group: 1,1%, 5,8% and 7,0%, respectively (p=0,043). Conclusion . Сomorbidity is an independent predictor of heart failure in MI, and their combination is associated with the most unfavorable in-hospital prognosis, regardless of the treatment strategy. The greatest advantage of PCI for reducing the hospital mortality rate was obtained in patients with comorbidity and without manifestations of AHF.