Arrythmia is a very common complication during the diagnostic heart catheterization and PTCA. So called benign types of arrythmia have to be distinguished from more severe forms such as ventricular tachycardia or ventricular fibrillation, resulting from the mechanic irritation of myocardium inflicted by the diagnostic catheter. In our catheterization laboratory heart rhythm disturbances are teh commonest complications occuring during the catheterization procedure. regarding the PTCA, so far we have not faced serious complications, but having in mind the number of the procedures performed in our hospital, these data cannot be considered as significant.