The effect of topical vasodilatation of sodium nitroprusside and papaverine has been studied in 106 consecutive patients who had undergone a coronary bypass operation by using internal thoracic artery. In sodium nitroprusside group there were 45 men, 8 women (ages ranged from 37 to 69, with a mean age of 54.88±8.09); and in papaverine group there were 47 men, 6 women (ages ranged from 39 to 74 with a mean age of 54.84±8.09) .There was no statistical difference between the groups in relation to age, gender, body surface area, and mean arterial pressure recorded during the measurement of internal thoracic artery flows. Free internal thoracic artery flow has been measured immediately after mobilization, before cardiopulmonary bypass, and in 64 patients during cordiopulmonary bypass and was simultaneously recorded with mean arterial pressure. These measurements were 1-60 ml/min (19.4±18.0), 7-150 ml/min (54.5±31.0) and 14-150 ml/min (70.2±35.0) in nitroprusside group; 1-100 ml/min (16.2±16.0), 3-120 ml/min (32.8±23.4) and 6-120 ml/min (41.9±29.5) in papaverine group respectively. Internal thoracic artery flow has been significantly increased by both of these vasodilators, and comparison of them revealed a significant difference in second and third flows in favour of sodium nitroprusside, whereas there was no statistically significance between the groups in the first flow. In conclusion sodium nitroprusside has been thought to be superior to papaverine in topical vasodilatation of internal thoracic artery.