Abstract:The influence of dietary fat on myocardial vulnerability to arrhythmia was examined using coronary artery occlusion and reperfusion in the anesthetised rat as a whole animal model of ventricular fibrillation and sudden cardiac death. Animals were fed a reference (REF) diet alone or supplemented 12% by weight with tuna fish oil (TFO) (rich in n‐3 fatty acids), sunflower seed oil (SSO) (rich in n‐6 fatty acids) or sheep perirenal fat (SF) (rich in saturated fatty acids). Feeding periods of 6, 12, and 18 months and a total of 108 rats were used. The incidence of ventricular fibrillation in occlusion was reduced from 46% of REF animals to 6% and 21% in TFO and SSO groups respectively and increased to 68% in the SF‐fed rats. The incidence of ventricular tachycardia was also reduced by TFO and SSO. The incidence of fibrillation on reperfusion of acutely ischemic myocardium (15 minutes occlusion) was significantly reduced by TFO only (12%, REF = 50%, SSO = 30%, SF = 70%). Severity of arrhythmias increased with age as did the extent of dietary influence. Mortality from fibrillation which only occurred in rats aged 12 months or older (REF = 13%) was increased by SF (43%) mainly in reperfusion (38%) but did not occur in TFO or SSO. These results indicate the potential benefit of dietary modification to include a higher proportion of polyunsaturated fat especially fish oil in reducing risk of sudden cardiac death. It is suggested that, in addition to their effects on atherosclerosis or thrombosis, dietary fats can directly influence myocardial vulnerability to arrhythmic stimuli through incorporation into myocardial membranes. (Aust NZ J Med 1989; 19: