 During open-heart surgery, blood flow is supported by a heart-lung machine that both pumps the blood and gives it oxygen. A problem associated with a heart-lung machine is the damage to some of the blood caused by protein in the blood cell sticking to the sides of the heart-lung machine tubing. This breakdown of the blood cell affects the platelets, which help the blood to clot. Use of the un-treated circuit will be phased out within the next few years, as newer technology is available. The use of coated tubing has been shown to decrease problems with post-operative bleeding in the adult population. No studies have been done on the pediatric population. We plan to perform a prospective, randomized study using the un-treated circuits used now, the Smart circuit tubing manufactured by Cobe Cardiovascular Inc., Arvada, CO and the PMEA circuit manufactured by Terumo Corporation, Tokyo, Japan. Randomization will be performed by the perfusionist the person that runs the heart-lung machine in charge of the case. No one else will be aware of which circuit is being used. There will be no changes in the operation of the heart-lung machine, anesthesia or the surgery because of this study. 