Objective: Coenzyme Q 10 (CoQ 10 ) levels are decreased in patients with cardiovascular diseases. The bioavailability of orally ingested CoQ 10 is limited to 2–3%, and long-term administration is required to increase the level of CoQ10 in myocardium for cardioprotection. Intravenous (IV) administration of solubilized CoQ10 immediately after coronary occlusion has been shown to increase myocardial levels rapidly and to protect against cardiac ischemia. The aim of this study was to determine the length of time following onset of myocardial infarction (MI) for which a single IV administration of CoQ 10 was cardioprotective. Methods: A single IV injection of solubilized CoQ10 (30 mg/kg, 1 ml/kg) or saline (1 ml/kg) was administered at either minute 60 or minute 180 after the onset of MI induced by coronary artery ligation in rats. Results: Twenty-one days after injection, CoQ 10 levels were still high in both the 60 and 180 minute groups. Rats treated with CoQ10 60 min after ligation had a significantly larger mass of viable left ventricle (LV) myocardium, limited LV dilatation, and improved cardiac contractile and relaxation capacity compared with controls. CoQ10 levels were significantly correlated with LV end-systolic volume (r=-0.65), end-diastolic volume (r=-0.56), ejection fraction (r-=0.67), and LV relaxation (r=-0.64) (p
