Vasospasm leading to thrombosis is a major cause of free flap failure. Flap blood flow may improve by application of vasodilating agents to the pedicle. The purpose of this study is to evaluate the effect of a novel S-nitrosylating agent, O-ethyl nitrite, on flap blood flow and pedicle vessels diameter in a rat model, after induction of vasospasm. Two hours after surgery, the arterial diameter was significantly (P < .05) dilated by treatment with O-ethyl nitrite, lidocaine, or lidocaine + O-ethyl nitrite. None of these treatments had a statistically significant effect on blood flow or venous diameter. Twenty-four hours following surgery, both O-ethyl nitrite- and lidocaine-treated groups had larger arteries than the control group (P < .05). The O-ethyl nitrite-treated animals also had significantly (P < .05) elevated blood flow compared with control animals, but lidocaine-treated animals did not demonstrate any improved flow at 24 hours. O-Ethyl nitrite may become clinically useful in microvascular surgery procedures.