Drug: Heparin
Heparin will be used as the intra-operative anticoagulant

Heparin is a drug that is widely used to prevent and treat blood clotting. However, heparin can also cause serious adverse events. Individuals undergoing cardiopulmonary bypass surgery are administered and therefore exposed to high doses of heparin. Studies have shown that up to 61% of cardiac bypass patients develop elevated levels of antibodies to heparin-PF4 after surgery. This immune response may activate blood platelets, possibly resulting in a blood clot. These clots most often develop in the legs and lungs, and may lead to a heart attack or stroke. The frequency of such a reaction has yet to be determined definitively. This study will evaluate the incidence of an immune response to heparin-PF4 that leads to the formation of blood clots in individuals who have had heart surgery.

Participants in this study will be recruited prior to a scheduled cardiac bypass surgery. They will first complete a structured pre-operative interview to collect baseline measures on demographics, comorbidities, history of heparin exposures, and prior thromboembolic events. Immediately prior to surgery, a blood sample will be taken to assess the individual's platelet count and level of antibodies to heparin-PF4. Following the operation, participants will be followed daily to assess heparin exposure, platelet counts, and any blood clotting. Subsequent blood samples will be taken 5 days and 1 month following the surgery to again evaluate the individual's platelet count and level of heparin-PF4 antibodies. Additionally, participants will undergo a structured interview at 1 and 3 months post-surgery to evaluate the incidence of outcomes related to heparin-PF4 antibodies.