Twenty-seven patients with post-infarction defect of the ventricular septum were examined: 27 had sounding of the right portions of the heart, 23 left ventriculography, 22 selective coronary angiography. The decision on the timing of the operation and the extent of surgery should be based on the findings obtained during intracardiac examination. If the grave condition of the patient is caused by a heavy drainage of the blood through the defect of the ventricular septum and by the volumetric overload of the heart then urgent surgery is indicated. On the other hand, if the severity of the patient's state is determined by mostly myocardial contractility disorders then the wait-and-see approach is appropriate. The intracardiac examination is a decisive method of the diagnosis of a post-infarction defect of the ventricular septum and is indicated for all patients with this disease. The extent of the examination is determined by the clinical state of the patient.