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The short- and long-term efficacy of oral encainide was studied in 14 patients with chronic high-frequency ventricular arrhythmias and in 14 patients with chronic frequent episodes of non-sustained ventricular tachycardia (NSVT). Encainide efficacy was assessed during a dose–titration perios and in a 36-month follow-up alos studying the drug effects on routine haematologic data and left ventricular function (LVF). During does–litration, encainide caused a 78.3% decrease in the average hourly frequency of isolated PVC and a 96.1% reduction in NSVT episodes in the two groups pf patients. On follow-up (11 patients in each group) the mean percentage redutions were 95.1% in isolated PVC and 99.7% in NSVT episodes. Encainide did not impair LVF as showed by the comparision of echocardiographic fractional shortening before and after 12 months of treatment. Minor adverse effects of encainide were dose-related visual disturbances in two patients. A major adverse effect was the apperance of sustained VT in one NYHA class IV patient. Oral encainide effectively reduces the frequency of PVC and NSVT, it does not impair left ventricular function and it is associated with infrequent minor side effects. Uncommon, but severe, side effects may appear in patients with marked impairment of left ventricular function. [ABSTRACT FROM PUBLISHER]