Background: Omega-3 polyunsaturated fatty acids (W-PUFAs) from fish oil reduce the risk of sudden death presumably by preventing life-threatening arrhythmias. Acutely administered omega 3-PUFAs modulate the activity of several cardiac ion channels, but the chronic effects of a diet enriched with fish oil leading to omega 3-PUFA-incorporation into the sarcolemma on membrane currents are unknown. Methods: Pigs received a diet either rich in W-PUFAs or in omega 9-fatty acids for 8 weeks. Ventricular myocytes (VMs) were isolated and used for patch-clamp studies. Results: omega 3-VMs contained higher amounts of omega 3-PUFAs and had a shorter action potential (AP) with a more negative plateau than control VM. In omega 3 VMs, L-type Ca2+ current (I-Ca,I-L) and Na+-Ca2+ exchange current (I-NCX) were reduced by approximately 20% and 60%, respectively, and inward rectifier K+ current (I-KI) and slow delayed rectifier K+ current (I-Ks) were increased by approximately 50% and 70%, respectively, compared to control. Densities of rapid delayed rectifier K+ current, Ca2+-activated Cl- current, and Na+ current (I-Na) were unchanged, although voltage-dependence of IN,, inactivation was more negative in omega 3 VMs. Conclusions: A fish oil diet increases omega 3-PUFA content in the ventricular sarcolemma, decreases I-Ca,I-L and I-NCX, and increases I-KI and I-Ks, resulting in AP shortening. Incorporation of W-PUFAs in the sarcolemma may have consequences for arrhythmias independent of circulating omega 3-PUFAs. (c) 2006 European Society of Cardiology. Published by Elsevier B.V. All rights reserved.