Background: A large body of evidence suggests that n-3 fatty acids from fish prevent fatal heart disease. They may be an effective and safe alternative to drug treatment for reducing the risk of arrhythmia and sudden cardiac death. Objective: We investigated the effect of n-3 fatty acids on heart rate and premature ventricular complexes (PVCs), a common form of arrhythmia that may trigger arrhythmias that are more life-threatening. Design: Patients (n = 84) with greater than or equal to 1440 PVCs/24 It in a previous Holler recording were randomly assigned to receive 1.5 g/d of either n-3 fatty acids or placebo. Two 24-h Holter recordings were made at baseline, and 2 were made after an intervention of approximate to14 wk. Results: Treatment did not significantly affect the number of PVCs. The number decreased in the fish-oil group by 867/24 h more than it decreased in placebo group (95% CI: -3187, 1453). However, the mean 24-h heart rate was significantly affected, decreasing in the fish-oil group by a mean of 2.1 beats/min more than it decreased in the placebo group (95% CI: -3.9, -0.3). Conclusions: Supplementation with 1.5 g n-3 fatty acids/d from fish does not substantially suppress the number of PVCs in a patient population with frequent PVCs. However, n-3 fatty acids decreased heart rate by 2.1 beats/min, a significant decrease that predicts a lower risk of sudden death.