OBJECTIVE: To determine the effects of n3-PUFA supplementation, in the dose used in the GISSI-Prevenzione study, on indices of heart rate variability (HRV) in patients following myocardial infarction (AMI). MATERIALS AND METHODS: Open label randomised single blind controlled trial. Thirty eight patients post AMI, stable on standard secondary prevention drug therapy were single blind randomised to receive either Omacor 1 g/day (n = 21) or usual care (n = 17). HRV indices (time and frequency-domain) were measured at baseline and following 3 months of treatment. RESULTS: At baseline there were no significant differences in clinical, biochemical or HRV indices between patient groups. After 3 months therapy there were no observed changes in measured HRV indices in either the Omacor supplemented or \'usual care\' groups. CONCLUSIONS: Three month supplementation of omega 3 PUFA (Omacor) 1 g/day has no effect on HRV is patients post AMI.