In addition to the preoperative Hb level, Chi-squared tests showed that age at the cutoff value of 2 years, RACHS-1 at the cutoff value of 3 scores, type of heart defect, clubbed fingers or toes, preoperative comorbidity and patent ductus arteriosus were significantly (P < 0.05) associated with the postoperative composite outcome, and SpO2 at the cutoff value of 74.1% (P = 0.084), pulmonary arterial hypertension (P = 0.092) and aortopulmonary collateral arteries (P = 0.095) were slightly associated with the composite outcome. The gene discussed is GSTM1; the disease is Patent ductus arteriosus.