Ventricular septum rupture (VSR) is a rare and dangerous mechanical complication of acute myocardial infarction (MI). Without timely diagnosis and surgical intervention, mortality in such patients reaches 90—100%. The authors describe VSR as a complication of acute MI in a 65-year-old patient with no anamnestic data of coronary artery disease. Due to intense chest pain and severe dyspnea, he was examined by emergency medical team, who diagnosed ST elevation acute inferior MI of the left ventricle, and the patient was hospitalized in cardiology department. In-hospital period was characterized by paroxysms of atrial fibrillation, twice cardiac arrest with cardiopulmonary resuscitation and several episodes of ventricular tachycardia. In 17 days after MI and 12 days after admission, a new systolic murmur appeared, and transthoracic echocardiography revealed 1.35 cm ventricular septum defect. Clinical and echocardiography data verified VSR, and the patient was transferred to cardiac surgery department.