In the 1980s, observational retrospective studies showed an inverse relation between coronary heart disease (CHD) and consumption of fish containing fatty acids that belong to the omega (ω)-3 family. Large case-control studies and prospective intervention trials consistently showed that ω-3 fatty acids supplementation lowers fatal myocardial infarction (MI) and sudden cardiac death. By analysing the strengths of the results of individual studies and how the meta-analyses agree with them, putting together relevant backgrounds, and identifying open questions, the following findings/directions emerge. (i) Dietary and non-dietary intake of ω-3 fatty acids reduces overall mortality, mortality due to MI, and sudden death in patients with CHD; (ii) Fish oil consumption directly or indirectly affects cardiac electrophysiology. Fish oil reduces heart rate, a major risk factor for sudden death; (iii) Among patients with implantable cardioverter defibrillators, ω-3 fatty acids do not reduce the risk of ventricular tachycardia/ventricular fibrillation and may actually be pro-arrhythmic; (iv) The consumption of ω-3 fatty acids leads to a 10-33% net decrease of triglyceride levels. The effect is dose-dependent, larger in studies with higher mean baseline triglyceride levels, and consistent in different populations (healthy people, people with dyslipidaemia, diabetes, or known cardiovascular risk factors); (v) Outcomes for which a small beneficial effect ω-3 fatty acids is found include blood pressure (about 2 mmHg reduction), re-stenosis rates after coronary angioplasty (14% reduction), and exercise tolerance testing. Major experimental data provide strength (biological plausibility) for these findings, and define directions for newer clinical trials with ω-3 fatty acids.