This study investigated whether postoperative low cardiac output and mortality in obstructed total anomalous pulmonary venous connection could be reduced by selective vertical vein patency. Fifty-eight patients undergoing rechanneling of total anomalous pulmonary venous connection between 1997 and 2006 were studied. The vertical vein was left patent in 27 patients (group I) and ligated in 31 (group II). Mean ages were 1.49 +/- 1.63 and 4.37 +/- 3.38 months for groups I and II, respectively. Operative mortalities were 29.1% and 7.4% for ligated and unligated groups, respectively (relative risk 1.75, 1.16-2.64, P = .036). Age younger than 1 month, obstructive total anomalous pulmonary venous connection, hypoplastic pulmonary veins, pulmonary hypertensive crisis, low cardiac output, and vertical vein ligation were significant risk factors for death according to logistic regression analysis. Patients with obstructed total anomalous pulmonary venous connection undergoing vertical vein ligation demonstrated predominant right ventricular dysfunction (relative risk 2.93, 1.28-6.73, P = .011), pulmonary hypertensive crisis (relative risk 2.90, 1.25-6.75, P = .013), and 3.28 times the risk of death (95% confidence interval 1.08-9.99, P = .032) relative to the unligated group. In a subset of patients with obstructed total anomalous pulmonary venous connection, an unligated vertical vein reduces pulmonary arterial pressure, decreases perioperative pulmonary hypertensive crises, provides a temporary pop-off valve during pulmonary hypertensive crisis, and improves survival by providing superior hemodynamics. The high mortality in the ligated group suggests that patients with obstructed total anomalous pulmonary venous connection with postbypass moderate pulmonary hypertension possibly should not undergo vertical vein ligation. We propose routine use of an adjustable ligature around the vertical vein in all patients with more than moderate post-bypass pulmonary hypertension, allowing gradual tightening in increments without multiple reoperations.