To analyze the characteristics of lipid metabolism in ischemic heart disease, lipoprotein composition, lipoprotein particle size, and activity of enzymes related to lipid metabolism (lecithincholesterol-acyltransferase (LCAT), lipoprotein lipase (LPL), hepatic triglyceride lipase (HTGL)) were studied and compared in patients with myocardial infarction and healthy controls. 24 inpatients with acute myocardial infraction (AMI), 22 outpatients with myocardial infarction in the past (OMI), and 22 healthy controls (C) were analyzed in the study. There was no significant difference in plasma lipid and lipoprotein cholesterol levels among the three groups. Analysis of the lipoprotein composition ratio (as the percentage composition in each lipoprotein fraction LDL and HDL) showed significantly higher HDL-TG% in the OMI group than in C group. HDL particle size was significantly larger in the AMI group than in the C group. LCAT activity was significantly lower in the AMI and OMI groups than in the C group. HTGL activity was lower in the AMI group than in the C group, while LPL activity showed no significant differences among the groups. It is well known that HTGL plays a fundamental role in the delipidation of HDL particle size (changing HDL2 to HDL3). Consequently, low HTGL activity in AMI patients may explain the high HDL-TG% composition and large HDL particle size in this group when compared to the corresponding composition and particle size in the control subjects. On the other hand, low LCAT activity in patients with myocardial infarction is more difficult to understand in light of its primary function. The activity of lipid transfer protein, another important component of lipid exchange reaction, must be analyzed together to elucidate better the mechanisms involved in the lipid metabolism in patients with ischemic heart disease.