Ventricular flutter evokes quick, haemodynamically little effective ventricular contractions. The still existing minimal circulation does not maintain the vital functions. Ventricular fibrillation is tantamount to the acute standstill of the cardiac circulation. If they are not treated, these malignant disturbances of the rhythm nearly always lead to death. Reentry processes or foci with rapid formation of impulses are discussed as responsible electrophysiological mechanisms. Warning arrhythmias are significant for the evocation of ventricular flutter and fibrillation. But the concept of the warning arrhythmias has no unrestricted validity. Thus also late involving ventricular extrasystoles can evoke ventricular fibrillation. Disturbances of intraventricular conduction are also significant for the development of ventricular fibrillation. In our own patients there were no disturbances of conduction only in 13.1% of the cases with ventricular fibrillation. Etiologically are of concern: acute myocardial infarction, chronic myocarditis, chronic ischaemic heart disease, current accidents, advanced stages of vitia and cardiomyopathies. Frequently ventricular fibrillation appears as paroxysmal form (paroxysmal uncoordinated ventricular tachycardia, "torsades de pointe") due to inhomogeneous repolarisation (prolongation of the QTU-time). Therapeutically only the immediate electro-shock therapy has a chance of success in ventricular flutter or fibrillation. Among our patients out of 61 patients with ventricular flutter and fibrillation 26 could be dismissed.