OBJECTIVE: To analyze the associations between marine n-3 polyunsaturated fatty acids (PUFAs) and blood pressure (BP), resting heart rate (HR), and heart rate variability (HRV) in a population highly exposed to methylmercury through the diet. METHODS: Concentrations of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) in erythrocytes membranes were measured in 180 French Polynesian adults (>/=18 years) residing in Tubuai, which is a community with a traditional lifestyle, or Papeete, which has a modern lifestyle. HRV was measured using a 2-hour ambulatory electrocardiogram (Holter). Resting HR and BP were measured using standardized protocols and pulse pressure (PP) was calculated as systolic BP - diastolic BP. The associations between n-3 PUFAs and the dependent variables were studied using simple and multiple linear regressions. RESULTS: Increasing DHA concentration was associated with lower resting HR (beta = -2.57, p = 0.005) and diastolic BP (beta = -1.96, p = 0.05) and higher HRV in multivariable models. Specifically, DHA was associated with high frequency (HF; beta = 0.19, p = 0.02) and the square root of the mean squared differences of successive R-R intervals (difference between two consecutive R waves; rMSSD; beta = 0.08, p = 0.03), which are specific indices of the parasympathetic activity of the autonomic nervous system. CONCLUSION: DHA was associated with lower BP and resting HR and higher HRV among French Polynesians who are also exposed to high methylmercury levels.