In this research study, we want to look at the difficulty in identifying infections in children who have heart surgery. We also want to look at differentiating between actual infections and the normal post-surgery course that patients go through. We use a number of tools in the Intensive Care Unit to pick out children at risk for an infection. These tools are the physical examination, a fever, white blood cell count, and C-reactive Protein (CRP) level. When a patient has an infection, they usually have a fever, have a high white blood cell count, and have an increased CRP level. However, these are not always correct. The identification of infection remains a challenge and the laboratory markers of infection (white blood cell count and CRP) that are used now are not perfect.