To compare postoperative outcomes in children undergoing cardiac surgery during the viral respiratory season and nonviral season at our institution. This was a retrospective cohort study and secondary matched case–control analysis. The setting was an urban academic tertiary-care children’s hospital. The study was comprised of all patients <18 years of age who underwent cardiac surgery at Johns Hopkins Hospital from October 2002 through September 2007. Patients were stratified by season of surgery, complexity of cardiac disease, and presence or absence of viral respiratory infection. Measurements included patient characteristics and postoperative outcomes. The primary outcome was postoperative length of stay (LOS). A total of 744 patients were included in the analysis. There was no difference in baseline characteristics or outcomes, specifically, no difference in postoperative LOS, intensive care unit (ICU) LOS, and mortality, among patients by seasons of surgery. Patients with viral respiratory illness were more likely to have longer postoperative LOS (p < 0.01) and ICU LOS (p < 0.01) compared with matched controls. We identified no difference in postoperative outcomes based on season in patients undergoing cardiac surgery. Children with viral respiratory infection have significantly worse outcomes than matched controls, strengthening the call for universal administration of influenza vaccination and palivizumab to appropriate groups. Preoperative testing for respiratory viruses should be considered during the winter months for children undergoing elective cardiac surgery.