Decreased 24-h heart rate variability (HRV) is associated with increased coronary mortality. The objective of this study was to examine the relation between plasma lipids and HRV (1) in men with a previous myocardial infarction (MI) and left ventricular dysfunction and (2) in healthy men. Forty seven men (mean age 63 years) with a previous MI and a left ventricular ejection fraction < or = 0.40 and 38 healthy men (mean age 37 years) were included. A 24-h Holter recording and fasting blood samples were performed in all the subjects. Plasma total-cholesterol and low-density-lipoprotein (LDL)-cholesterol were inversely correlated with 24-h HRV in both groups. Plasma cholesterol remained significantly inversely correlated to the 24-h HRV in a stepwise multiple regression analysis. The men were dichotomized according to the mean plasma cholesterol in the study population which was 6.2 mmol/l in patients with a previous M1, and 5.2 mmol/l in the group of healthy men. In both groups, men with plasma cholesterol levels above the mean had the lowest HRV. In conclusion, the data suggest, that hypercholesterolaemia is associated with a decreased 24-h HRV in men with and without ischaemic heart disease, suggesting an increased risk of sudden cardiac death.