Based on pharmacodynamic and pharmacokinetic studies in 42 patients with paroxysmal and extrasystolic abnormalities of the rhythm it was established that disopyramide phosphate (ritmilen) is an effective antiarrhythmic agent for atrial fibrillation paroxysms. The drug exerts negative, chronotropic, dromotropic and inotropic effects, especially upon intravenous injections for removal of atrial fibrillatin paroxysms. Ritmilen moderately reduces the blood pressure. When used for removal of atrial fibrillation paroxysms ritmilen is effective in doses of 1.2-1.7 mg/kg intravenously and in doses of 2.5-3.8 mg/kg per os. In patients with chronic ventricular premature heart beat the single effective drug doses amount to 0.61-1.7 mg/kg. After oral use the ritmilen concentration in blood plasma is lower than after intravenous use in adequate doses. No relationship has been found between the drug antiarrhythmic effect and blood plasma concentration.