**4. Population and sample**

We included all patients with univentricular hearts who underwent Fontan operation. We reviewed the records of the patients included in the univentricular heart protocol and database service Congenital Cardiac Surgery Cardiovascular Clinic of Santa Maria de Medellin (Colombia), identifying all patients undergoing the Fontan operation with technique total cavopulmonary anastomosis between 1994 and 2010.

We reviewed the medical records, operative reports and echocardiograms.

**Monitoring.** All patients who survived the Fontan surgery underwent clinical and echocardiographic follow-up. We also obtained information about procedures performed after surgery, medication use and functional ability (classified according to New York Heart Association guidelines), interviewing parents and cardiologists caring for for each patient.
