The authors had 75 patients with myocardial infarction under observation. After the 15th day of the disease various disorders of cardiac rhythm and conductivity were revealed in 85% of patients during cardiomonitor surveillance. The most frequent occurrences were ventricular extrasystole (72.5%), sinus bradycardia (40%) and atrial extrasystole (37.5%). Primary ventricular fibrillation was noted in 4 (5.3%) patients two of whom were resuscitated. In 50 patients with myocardial infarction of more than one month duration disorders of cardiac rhythm during physical load were studied (dosed walking under telectrocardiographic control and/or on a treadmill). During dosed waling 28% of patients developed arrhythmia or it was intensified (sinus tachycardia was not taken into account). During a load on a treadmill such changes were encountered in 30% of patients. A favourable effect of treatment with cordarone was produced in most patients with ventricular extrasystole some of whom were resistant to lidocain treatment. A good effect was produced in some patients by means of the pulsnorma or rythmodan. Beta-adrenergic blocking agents as well as cordaron and isoptin were effective in atrial extrasystole and sinus tachycardia. Hyperbaric oxygenation was used in 14 patients with disorders of rhythm. Disappearance of arrhythmia or considerable improvement was registered in 11 patients after treatment consisting of 10-12 procedures.