Coronary artery ligation (CAL) was used to produce an in vivo model of cardiac arrhythmias and myocardial infarction using anaesthetized male Hooded Wistar rats which had been fed for 6-7 or 18-20 months on either a standard reference diet alone or supplemented (12% w/w) with sunflower seed oil (linoleic acid rich) or sheep kidney fat (linoleic acid poor). The number of ventricular extra beats and duration of tachycardia or fibrillation in the 30-min postligation was increased in sheep kidney fat-fed rats. Infarct size 4 h postCAL was reduced in sunflower seed oil-fed rats. Arrhythmias, infarct size, and dietary-induced differences were increased with age. The diets employed produce changes in myocardial membrane phospholipids which could result in altered prostaglandin production. These results show that in the rat (as in man), age and dietary saturated fat are risk factors for sudden cardiac death and myocardial infarction and suggest that the rat is a useful model for the investigation of dietary interventions in heart disease.