The relation between subcutaneous adipose tissue fatty acid composition and serious ventricular arrhythmias during acute myocardial infarction was studied in 2 groups of patients. In group 1 (n = 42), studied retrospectively, patients with ventricular fibrillation or tachycardia had a higher concentration of long-chain saturated fatty acids than those without (32.5 ± 0.8% vs 29.7 ± 0.4% [mean ± standard error of the mean], p < 0.01). In a prospective study, patients with arrhythmias (n = 106) had higher levels of long-chain saturated fatty acids (32.1 ± 0.5% vs 30.7 ± 0.4%, p < 0.05) and of stearic acid (4.9 ± 0.2% vs 4.4 ± 0.1%, p < 0.02) and a lower concentration of palmitoleic acid (7.3 ± 0.3% vs 8.1 ± 0.2%, p < 0.005). When peak plasma creatine kinase concentrations were included with the individual fatty acid levels in a multiple logistic regression, only creatine kinase correlated significantly with ventricular arrhythmias (p < 0.01). Thus, saturated fatty acids in cardiac membranes may lead to greater vulnerability to ventricular arrhythmias, although infarct size is the only statistically significant predictor after multiple regression analysis.