Sudden Cardiac Death resulting from sustained ventricular fibrillation or malignant cardiac arrhythmia has been linked to the type of dietary fat intake in several economically well developed countries where high levels of saturated fatty acids are common. Experimental studies with the small non-human primate marmoset monkey have clearly demonstrated the health benefit of substituting polyunsaturated fatty acids (PUFA's) for dietary saturated fatty acids. Heart rate and blood pressure are lowered, while the left ventricular ejection fraction and the electrical threshold for the induction of ventricular fibrillation are both increased after prolonged feeding of PUFA enriched diets. All these changes in heart function reduce the risk of developing malignant cardiac arrhythmias. The fatty acid composition of cardiac membrane phospholipids is profoundly altered by these changes in dietary lipid intake. In particular the proportions of arachidonic acid (AA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are altered in such a way that the production of myocardial eicosanoids is affected. Although the changes in proportion of these long-chain PUFA's in cardiac phosphatidyl ethanolamine and phosphatidyl inositol are not identical, the shift in balance between these substrates or inhibitors of cyclo-oxygenase activity leads to relatively greater production of prostacyclin (PGI2) than thromboxane (TXA2).(ABSTRACT TRUNCATED AT 250 WORDS)