This study has the following research questions:
1. What is the reproducibility of ventricular systolic function measurements (including ventricular strain) in Fontan patients using echocardiography (Echo) and cardiac magnetic resonance imaging (CMR)?
2. What is the reproducibility of ventricular diastolic function measurements (including tissue Doppler and strain rate) in Fontan patients using Echo and CMR?
3. Is there a correlation between ventricular function measurements and circulating biomarkers (including galectin-3 levels, NT-proBNP, ST2, and MELD-XI score)?
