Evaluation of Pro-Inflammatory Leukocyte Activity in Patients Undergoing Cardiac Surgery

This study is measuring how the immune system — specifically white blood cells called leukocytes — becomes activated during complex heart surgery that uses a heart-lung bypass machine (cardiopulmonary bypass, or CPB). When blood flows through the bypass circuit, it can trigger inflammation, which may contribute to complications after surgery. Understanding exactly how this inflammation is triggered and progresses could lead to better ways to protect patients. Participants will have blood samples taken at multiple time points before, during, and after surgery. The study is observational — researchers will not change how the surgery is performed or prescribe any additional treatments. You may be eligible if you: - Are a patient of any age scheduled for a complex cardiac surgical procedure using cardiopulmonary bypass (CPB) You may NOT be eligible if you: - Are undergoing an emergency procedure with less than 1 hour available to review and sign the consent - Are in a critically ill (moribund) condition — ASA classification 5 - Have a hematological or oncological (blood or cancer) disease - Are a Jehovah's Witness (due to potential blood handling requirements) Talk to your doctor to see if this trial is right for you.