SummaryProcain-amide was administered to 28 patients with various cardiac arryth- mias. It was only efficacious in ventricular extrasystcles using a dosage of 3 to 4 gr per day. The dose required when injected intravenously varied from 300 mgr to 1 gr.1) One observes the disappearance of all the ventricular extrasystoles, but this effect is transitory. The action on auricular extrasystoles is less constant.2) Sinusal rhythm is re-established in one case of paroxystic nodal tachycardia and in one case of ventricular paroxystic tachycardia.3) One case of auricular paroxystic fibrillation is stoped; in 3 cases of chronic fibrillation arrhythmia persists.4) In 2 patients with chronic auricular fibrillation and ventricular extrasystoles caused by digitalis the extrasystoles disappear but fibrillation persists.5) Auricular fibrillation of long duration is obtained experimentally in 8 dogs. In all cases, sinusal rhythm is re-established by injection of too to 200 mgr of procain-amide.6) In dogs also, electrocardiographic alterations due to high dosage ol procain-amide are studied.7) From these various observations practical conclusions are drawn concerning the indications and dosage of procain-amide in cardiac arrhythmias.