The effect of long-term feeding of various dietary fats and oils on cardiac arrhythmia was studied in an animal model of sudden cardiac death. After confirmation that a dietary supplement of saturated animal fat (SF) increased the animals' susceptibility to develop cardiac arrhythmia under ischemic stress whereas the polyunsaturated fatty acids of sunflower seed oil (SSO) reduced this susceptibility, we found that diets supplemented with either chemically refined palm oil (PO-I) or physically refined palm oil (PO-II) gave results that were generally intermediate in value between the SF and the SSO groups. However, during reperfusion of a previously ischemic heart, both PO-I- and PO-II-supplemented diets appeared to be as effective as SSO in reducing ventricular premature beats. In addition, the incidence of animals displaying severe ventricular fibrillation was much less after palm-oil feeding than it was after SF feeding. These preliminary results warrant further investigation of the potential antiarrhythmic effects of commercial palm oil.