Objective: The internal thoracic artery (ITA) is currently the preferred conduit for myocardial revascularization; however, perioperative vasospasm of the ITA may cause morbidity. Pedicle preparation and pharmacological vasodilatory treatment vary greatly. This clinical study was performed in order to define the effectiveness of two different applications of sodium nitroprusside as vasodilating agent. Methods: Eighty-six consecutive patients whose left ITA was mobilized only by one surgeon for elective coronary artery bypass graft operations were randomly divided into two groups. The ITA was allowed to bleed freely, and the flow was determined (flow 1) in group I (n=42) 3 mg sodium nitroprusside in 10 ml of 5% dextrose solution was sprayed with pressure on the pedicle with a thin 25 gauge needle. In group II (n=44) half of the solution was sprayed in the same manner, and the other half of the solution was injected into the pedicle in the periarterial tissue along the length of the pedicle. Free flows of the ITA were registered before cardiopulmonary bypass (flow 2) and also just prior to performing ITA anastomosis to the left anterior descending artery (flow 3). With each measurement hemodynamic parameters and the time between measurements were recorded. Results: No statistically significant differences were found between the groups in respect to sex ratio, age, body surface area, heart rate 1 and 2, mean arterial pressure 1 and 3. There was no significant difference in the initial flow among groups. Significant differences were noted in the second flow measurement (p