The object of the present investigation was the discovery of the arrhythmias in the patients with prolapse of the mitral valve (PMV), the types of arrhythmias, the factors favouring them, the therapy used. In a group of 126 patients suffering from PMV, 25 had mitral insufficiency, and 48% of the cases had arrhythmias too. The ventricular arrhythmias existed in 18 patients, in the most of them as ventricular extrasystoles. Only in 2 cases, ventricular paroxysmal tachycardia was noticed, and only one case of ventricular fibrillation was recorded. The following conclusions were drawn from the study: the increase of arrhythmias is low, their appearance is correlated with mitral insufficiency, ventricular arrhythmias are predominant, the majority are benign, they are more frequent than in the patients with neurovegetative dystonia (if considering the prolapse associated with systolic murmur), necessity of periodic control for discovering the cases with high risk of ventricular arrhythmias with malignant potential.