Background Although the small dense low-density lipoprotein (sd-LDL) is associated with hypertriglyceridemia, more than 60% of myocardial infarction (MI) patients are normotriglyceridemic in the fasting state. This study was aimed to investigate the relationship between the low-density lipoprotein (LDL) phenotype and postprandial hyperlipemia (PPL) in MI patients. Methods and Results Oral fat tolerance tests were performed in 71 patients with acute MI and fasting triglyceride concentrations below 200 mg/dl. Postprandial changes in the LDL particle diameter (LDL-PD) and lipids over a 6-h period after a meal were compared among 4 groups of patients classified according to fasting triglyceride levels (A, B as <150, and C, D as ≥150) and postprandial triglyceride levels (A, C as <230 and B, D as ≥230). Although fasting concentrations of triglyceride and remnant-like particle (RLP)-triglyceride were significantly higher in group C than in group B, the areas under the curves of the RLPs were significantly higher in group B. The triglyceride-to-cholesterol ratio in the RLPs was significantly higher in the PPL group than in the nonPPL group postprandially. The prevalence of sd-LDL (LDL-PD ≤25.5 nm) was significantly higher in group D but similar between groups B and C (23%, 42%, 50% and 83% in groups A, B, C and D, respectively). Conclusion These results suggest that postprandial accumulation of triglyceride-rich lipoproteins is strongly associated with sd-LDL in MI patients without hypertriglyceridemia. (Circ J 2004; 68: 1165 - 1172)