The aim of this study was to evaluate the impact of blood transfusion on bloodstream infections. This study included 2764 patients who underwent isolated coronary artery bypass grafting. Blood cultures were drawn in 27.9% of patients and were positive in 3.5% of them. Blood transfusion before blood cultures were drawn (4.7% vs 1.2%, odds ratio 3.75, 95% confidence interval 1.11–12.67) and deep sternal wound infection/mediastinitis (20.0% vs 2.8%, odds ratio 7.43, 95% confidence interval 2.72–20.32) were independent predictors of a positive postoperative blood culture. Positive blood culture increased the risk of 5-year mortality (among patients with blood cultures drawn: 44.7% vs 19.6%, adjusted hazard ratio 2.10, 95% confidence interval 1.18–3.71). Exposure to blood products may increase the risk of bloodstream infection after cardiac surgery. Positive blood cultures after coronary artery bypass grafting are associated with poor late survival. These findings require validation in prospective studies.