Background and Objectives: Endoscopic vessel harvesting (EVH) traditionally uses carbon dioxide (CO2) gas for insufflation. The CO, based on government regulations is bone dry and room temperature. All previous EVH studies use this type of unconditioned gas. It is hypothesized that by changing the quality of CO, gas differences may occur that are attributable to dry gas versus wet gas exposure. Methods: A comparison of the effect(s) of traditional dry CO, gas compared to humidified exposure was done using a porcine model and evaluated in a double-blind randomized controlled fashion. Results: Vessels exposed to traditional dry cold gas had morphologic and structural changes noted on histologic evaluation. This included desiccation changes of the tunica adventitia desiccation and tunica media collagen and elastin. Vessels exposed to dry gas showed 10% to 12% contraction and constriction with tortuous changes to the intima and endothelial lining that were progressive with increasing volumes of gas exposure. No desiccation or morphologic changes were seen with humidified warmed gas produced using the Vessel Guardian. Conclusions: Traditional dry cold CO, caused vascular tissue damage extending from the adventitia to intima, changing the vessel in morphologic and structural configuration. With the Vessel Guardian humidified warmed, gas maintained vessel morphology and integrity by preventing desiccation. Changing the quality of CO, from dry and cold to wet and warm may offer clinical utility for a better quality conduit for coronary artery bypass graft procedures.