Omega-3 polyunsaturated fatty acids such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) have beneficial effects on the heart and vasculature. We tested the hypothesis that 6 weeks of dietary supplementation with DHA (2.0 g/day) and EPA (3.0 g/day) enhances exercise-induced increases in brachial artery diameter and blood flow during rhythmic exercise. In seven healthy subjects, blood pressure, heart rate and brachial artery diameter, blood flow, and conductance were assessed before and during the last 30 s of 90 s of rhythmic handgrip exercise (30% of maximal handgrip tension). Blood pressure (MAP), heart rate (HR), and brachial artery vascular conductance were also determined. This paradigm was also performed in six other healthy subjects who received 6 weeks of placebo (safflower oil). Placebo treatment had no effect on any variable. DHA and EPA supplementation enhanced contraction-induced increases in brachial artery diameter (0.28+/-0.04 vs. 0.14+/-0.03 mm), blood flow (367+/-65 vs. 293+/-55 ml min-1) and conductance (3.86+/-0.71 vs. 2.89+/-0.61 ml min-1 mmHg-1) (P<0.05). MAP and HR were unchanged. Results indicate that treatment with DHA and EPA enhances brachial artery blood flow and conductance during exercise. These findings may have implications for individuals with cardiovascular disease and exercise intolerance (e.g., heart failure).