Although the majority of cases of acute myocardial infarction are caused by atherosclerotic coronary artery disease (CAD), it can also occur in people with normal coronary arteries. One of the possible mechanisms causing myocardial infarction with normal coronary arteries (MINC) is transient occlusion of the infarct-related artery owing to platelet hyperactivity and thrombosis. Mean platelet volume (MPV), an indicator of platelet activation, has been shown to be elevated in patients with unstable angina and myocardial infarction in the setting of obstructive CAD. However, the value of MPV in patients with MINC is not known. The aim of this study was to assess the MPV in patients with MINC. We retrospectively studied 47 patients with MINC, 63 patients with myocardial infarction resulting from single coronary artery disease (MISC) and 55 control subjects. MPV values were recorded in all study patients and control subjects. The MPV values of patients with MINC and MISC were significantly higher than those of the control group (9.1 +/- 1.8 and 9.4 +/- 1.0 versus 8.3 +/- 1.4 fl; p < 0.05 and p < 0.001, respectively). There were no significant differences in MPV values between the MINC and MISC groups. We show for the first time that MPV is significantly higher in patients with MINC compared with control subjects. Concurring with previous studies, we also show that MPV is significantly higher in patients with MISC compared to control subjects.