Flecainide and propafenone are antiarrhythmic drugs of the class 1C (Vaughan and Williams) commonly used for ventricular arrhythmias. The purpose of the present study was to evaluate the efficacy of these drugs in 170 consecutive patients with ventricular arrhythmias who referred to our cardiological ambulatory. The study population was divided into two groups according to the absence (group A,82 patients) or presence of organic heart disease (group 1B: 51 patients with left ventricular ejection fraction (LVEF) >35%; group 2B: 37 patients with LVEF<35%). Ventricular arrhythmias were evaluated with a 48 hours Holter monitoring at baseline, and with a control 24 hours Holter monitoring at 15 days (for optimizing the dosage), at 5 months and at 10 months from the beginning of antiarrhythmic therapy. Patients of group A were randomly assigned to antiarrhythmic treatment (flecainide 150-300 mg/die or propafenone 450-900 mg/die). For patients of group B, such choice was leaded by the clinical and strumental data (32 patients were treated with flecainide, 56 patients with propafenone). In the 160 patients who ended the 10 months follow-up, we observed the following results: patients of group A showed a mean percentage reduction in incidence of premature ventricular complexes (PVC) after therapy in comparison to basal conditions of 93% and 89% with flecainide and propafenone, respectively, after a treatment of 5 months (p < 0.001); after 10 months mean percentage reduction of PVC was 91% with each drug (p = n.s.); complex ventricular events (CVE) were reduced of 90% and of 100% after 5 and 10 months, respectively, of treatment with flecainide and of 100% both after 5 and 10 months of treatment with propafenone (p = n.s.) -- patients of group 1B showed a mean percentage reduction of PVC of 87% and 84% after 5 and 10 months, respectiively, of treatment with propafenone (p = n.s.); after 5 months of therapy mean percentage CVE reduction was 66% with flecainide and 86% with propafenone (p < 0.001); after 10 months this mean reduction was 53% with flecainide and 73% with propafenone (p < 0.001). -- patients of group 2B showed a mean reduction of PVC of 59% and 58% after 5 and 10 months of therapy with flecainide, and of 65% and 67% after 5 and 10 months of therapy with propafenone (p = n.s.); CVE were reduced of 28% with flecainide and of 47% with propafenone after 5 months of treatment (p < 0.001) and of 36% with flecainide against 52% with propafenone after 10 months (p < 0.01). In the present study there was no significant difference between the two drugs in terms of tollerance and collateral effects (8% with flecainide vs 7%, with propafenone). Our results confirm the efficacy of the 1C class drugs in the treatment of "essential" ventricular arrhytmias. This efficacy appears reduced in non selected patients with organic heart disease. In these latter patients propafenone has shown more efficacy than flecainide in reducing CVE.