 Previous human observational studies and clinical trials provide strong indications that n-3 PUFA from fish can prevent cardiovascular disease. Striking is that these studies show a strong relation between n-3 PUFA and sudden death, but not between n-3 PUFA and non-fatal heart disease. Sudden death is one of the most common and often the first manifestation of coronary heart disease. The majority of sudden deaths are directly caused by acute ventricular arrhythmia. Our hypothesis is that n-3 PUFA prevents sudden death by suppressing life-threatening cardiac arrhythmia. Therefore, we investigate in a randomized controlled clinical trial whether supplemental intake of n-3 PUFA from fish can reduce the incidence of life-threatening cardiac arrhythmias. Our population consists of patients with an implantable cardioverter defibrillator ICD, because this device records all arrhythmic events in a memory chip. As the ICD enables continuous monitoring of events in nonhospitalised patients, this population is very suitable for testing a possible antiarrhythmic effect of n-3 PUFA. The objective of the SOFA trial is to investigate the effect of fish oil on the incidence of recurrent ventricular arrhythmia in patients with an ICD. The SOFA is a randomised, parallel, placebo-controlled, double-blind intervention study which is currently being carried out in 26 cardiology centers in Europe. Five hundred forty six patients with an ICD are randomised to receive either 2gd of fish oil or placebo oil for a period up to 12 months. The primary outcome is spontaneous ventricular tachyarrhythmias as detected by the ICD or all-cause mortality within 12 months. 