A long-term study of the efficacy and tolerance of propafenone was carried out in cases of severe chronic ventricular extrasystoly in elderly patients (age 70). The patients included presented more than 1,500 ventricular extrasystoles per 24 hours with severe criteria. After the Holter performed upon inclusion, 450 mg/d of propafenone were prescribed (900 mg/d in 4 cases). The Holter tests were then repeated at D8, D30, D60, D180, D360, with possible modification of the dosage. 16 patients were then studied, and the study completed its half of them in one year. The efficacy, evaluated by at least an 83 p. cent decrease of the number of ventricular extrasystoles with disappearance of complex forms, was excellent in 12 out of 16 patients, non-existent or insufficient in 2 patients. The arrhythmia was aggravated in 2 cases. In addition, the efficacy of propafenone was maintained in the 8 patients who responded to the treatment and were followed for one year. A poor tolerance (conduction disorders, aggravated arrhythmia) was noted in 7 patients (44 p. cent of the cases). Conduction disorders were present with a propafenone dosage or on preexisting conduction anomalies. Five deaths occurred during the study, unrelated to the treatment. At a dose of 450 mg/24 h, propafenone is therefore effective, most of the time, effective in the treatment of severe ventricular extrasystoly in elderly patients, with a rather good tolerance, and a long-term efficacy. Higher doses only improve minimally the efficacy and are much less well tolerated.