ranolazine is a new antianginal drug that is postulated to act through blocking of cardiac late sodium channels and improvement in cardiac blood flow. the present study has been carried out to investigate its possible effect on microcirculation of normal and diabetic rats’ cardiac muscle. methods: normal and diabetic rats were anesthetized. the chest was opened and a surface laser doppler flowmeter probe was sutured on the left ventricle next to the left anterior descending branch of the coronary artery. after 30 minutes of animal adaptation, baseline flow was recorded. thereafter, ranolazine was injected intravenously (10 mg/kg) through the jugular vein and the changes in the cardiac blood flow were measured every 5 minutes for 30 minutes. systolic blood pressure and heart rate were also recorded. results: although, injection of ranolazine resulted in some reduction of cardiac blood flow, no significant changes were observed in normal and diabetic animals. ranolazine had no significant effect on systolic blood pressure of either groups studied. nevertheless, it caused a mild but statistically significant increase in the heart rate of diabetic and normal rats. conclusion: in conclusion, in normal and diabetic rats, no evidence of improvement in intramyocardial blood flow by ranolazine was obtained.