Heat flow in the neck was simulated in FLUENT to study countercurrent effects of cooling blood in the carotid artery during selective brain cooling. The simulation was performed in order to verify Zhu?s theory (used as a basis for our methodology) and to determine the contribution of countercurrent exchange by comparing results to a heat flow model without exchange. The surface temperature of the neck and flow rates within the vessels were varied to determine the specific effects of countercurrent exchange. With ambient skin temperature (25?C) and normal blood flow rate (120 ml/min); our model demonstrates that the average temperature of the arterial blood reaching the brain drops by 1.18?C while traveling through the neck. The effect of the countercurrent exchange alone contributes 0.88?C to this temperature decay. Placing an ice pack on the neck surface can further decrease the arterial blood temperature by as much as 1.0?C. This indicates that placing an ice pack on the neck does aid in selective brain cooling and that countercurrent exchange has a significant impact in cooling as well. The overall temperature drop of blood between the inlet to the carotid artery and the outlet was found to decrease with increasing blood flow rates and surface temperatures, verifying the trends modeled in Zhu?s analysis. Zhu?s theoretical study, however showed a temperature drop of 0.35?C at a blood flow rate of 240 ml/min with vein inlet blood temperature at 29?C and neck temperature at 19?C whereas ours showed a temperature drop above 0.85?C. Sensitivity analysis was performed to test the stability of our solution and to discover factors that might affect arterial outlet temperature. The factors that had the most influence on penetration depth were the specific heat of the blood and varying the thermal conductivity of the tissue. This project could be expanded upon by considering more variations in geometry, such as center-to center spacing, vessel eccentricity and modeling multiple vessels. This would allow for a better model of the true behavior of heat flow in the neck.