BACKGROUND: Patients at our pediatric outpatient clinic were offered 24-h Holter electrocardiogram (ECG) before and after 3-month period of dietary supplementation with omega-3 fatty acids to monitor the effect on heart rate variability (HRV) and arrhythmias. METHODS: The study included 17 children (mean age: 11.6鈥?/-鈥?.9鈥痽ears) with >1% premature ventricular contractions (PVC) at baseline. 24-h Holter ECG monitoring was performed before and after omega-3 fatty acid supplementation (mean duration: 143鈥痙ays). RESULTS: Compared with 86 age-matched healthy control children, baseline HRV was significantly reduced and mean heart rate was significantly increased in children with frequent PVC. After omega-3-fatty acid supplementation, the mean heart rate decreased from 92.6鈥?/-鈥?.4鈥痓pm to 83.9鈥?/-鈥?.9鈥痓pm (p鈥?鈥?.001), while global HRV showed a significant increase [standard deviation of all NN intervals (SDNN): 148.1鈥?/-鈥?4.4鈥痬s vs. 126.5鈥?/-鈥?9.3鈥痬s, p鈥?鈥?.022)]. Enhanced vagal activity was indicated by significantly higher square root of the mean of the sum of the squares of differences between adjacent NN intervals (rMSSD) (42.3鈥?/-鈥?2.6 vs. 33.2鈥?/-鈥?4.8; p鈥?鈥?.0003). PVC percentage significantly decreased by 45% (6.9鈥?/-鈥?.0% vs. 12.1鈥?/-鈥?.2%; p鈥?鈥?.014). CONCLUSIONS: Omega-3-fatty acid supplementation caused a 45% reduction in frequent PVC in children with structurally healthy hearts. This antiarrhythmic effect was likely attributable to improved autonomic function, which is consistent with previous findings in children with obesity, attention deficit disorder, and short stature.