Cardiovascular disease is the leading cause of death in the United States. Despite decades of care path improvements approximately 30% of heart attack victims die within 1 year after their first heart attack. Animal testing has shown that mild hypothermia, reducing tissue temperatures by , has the potential to save heart tissue that is not adequately perfused with blood. This paper describes the design of a cooling guide catheter that can provide rapid, local cooling to heart tissue during emergency angioplasty. Using standard materials and dimensions found in typical angioplasty guide catheters, a closed-loop cooling guide catheter was developed. Thermal fluid modeling guided the interior geometric design. After careful fabrication and leak testing, a mock circulatory system was used to measure catheter cooling capacity. At blood analog flow rates ranging from 20 ml/min to 70 ml/min, the corresponding cooling capacity varied almost linearly from 20 W to 45 W. Animal testing showed 18 W of cooling delivered by the catheter can reduce heart tissue temperatures rapidly, approximately 3° in 5 min in some locations. Future animal testing work is needed to investigate if this cooling effect can save heart tissue.