Therapeutic effectiveness of a new long-acting antiarrhythmic preparation was evaluated in 31 patients with sustained premature ventricular beats. After an observation period, a 24 hours Holter monitoring was performed. A group (21 patients) was treated with dihydrochinidine 250 mg twice a day; another group (11 patients) was treated with 500 mg twice a day. In the latter group was determined basal chinidinemia on the first and third day. A 24 hours Holter monitoring was repeated on the fourth day. In the first group we reached a 77.4% reduction of the arrhythmia: not enough, however, to agree with established statements. We reached a larger reduction (84.7%) with higher doses (1000 mg daily). This drug was well tolerated in both groups.