SummaryThrough their inhibitory action on conduction and changes they produce on myocardial excitability, cardiotonic glucosides play a leading part in the treatment of many disturbances of heart rhythm. Ventricular tachycardia and auriculo- ventricular block constitute the only classical contra-indications to their use Their direct cardiotonic effects are always desirable when arrhythmia induces heart failure.1)In auricular flutter,digitalis is essential; it is the only drug to restore sinus rhythm in more than half of the cases. Dosage should be large enough to impregnate heart muscle correctly. The only contra-indication is flutter with very slow ventricular rhythm or with conduction disturbances. Digitalis is the treatment of choice in the prevention of recurrences.2)Inpermanent auricular fibrillation,digitalis is indicated for the control of ventricular rhythm when quinidinc is contra-indicated or has failed. Although anticoagulant therapy must often be associated with digitalis, cardiotonic glucosides are usually better tolerated than quinidine in chronic cases. Their place in the treatment of paroxystic tachycardia is less important for they tend to maintain this type of arrhythmia.3)In supraventricular tachycardia,when active intervention is mandatory, digitalis constitutes a safe therapy, which is probably more efficient than peroral quinidine treatment, and less dramatic than cholinergic drugs. Chronic digitalization efficiently prevents recurrences. Digitalis is strongly advocated in supraventricular tachycardia in infants and children.4)Ventricular tachycardiaconstitutes classical contra-indication to the use of digitalis, except in very rare cases, where other drugs have failed.5)Auriculo-ventricular blocksare also contra-indications, unless heart failure has supervened. In such cases, digitalis therapy should he carefully supervised.6)Digitalis induced arrhythmiasrequire interruption of treatment.The use of digitalis in cardiac arrhythmias necessitates regular clinical and electrocardiographic supervision, usually in specialized environment, with sometimes the addition of K or antifibrillating agents, and the choice between the various glucosides. Their handiness and efficiency, in function of precise indications, constitute the main qualities of these often irreplaceable drugs.