Single ventricle defects make up the severe end of the congenital heart disease spectrum. The Fontan operation leads to a complete redirection of systemic venous blood outside of the heart and directly into the lungs. Patients with single ventricles suffer from multiple complications. Their survival has improved over the past decades, but is still severely compromised compared to the general population.

Their evaluation includes echocardiography and functional status by history and/or exercise testing. In longer intervals or if echocardiography does not allow visualization of all cardiovascular structures, cardiac magnetic resonance (CMR) is employed. Many patients also undergo more invasive cardiac catheterization.

In single ventricle patients, cardiac imaging has to address the questions of the patency of the Fontan pathways, i.e. all systemic veins, the Fontan conduit, and the pulmonary arteries, and of the function of the single ventricle (including myocardial function and valve function).

By using conventional imaging methods in Fontan patients, Ghelani et al. identified a CMR-based ventricular end-diastolic volume of > 125 ml/m2 and an echocardiographic global circumferential strain (GCS) value of higher than -17% to be strong predictors for a combined adverse outcome of death or heart transplantation. While interobserver reproducibility of single ventricle ejection fraction is similarly high by echocardiography, CMR is better in reliably measuring ventricular mass and diastolic volume and can provide additional information by MR feature tracking (strain), T1 mapping, and 4D flow measurements. Several substances that can be measured in the peripheral blood are being increasingly investigated as biomarkers of heart failure.

In conclusion, several advanced CMR sequences and new biomarkers have a potential role in the assessment and risk stratification of single ventricle patients. Every single published study has elucidated a particular use and aspect of these parameters, but broader correlations and prognostic values are still unclear.

The investigators hypothesize that myocardial strain (by feature tracking), myocardial fibrosis (by T1 mapping), and intracardiac flow disturbances (by 4D flow) along with biomarkers are diagnostic for single ventricle dysfunction and correlate with known prognostic factors.

This is a single center, prospective, observational cohort study. There will be no randomisation or blinding. Study setting: outpatients, cardiology clinic and radiology department, academic hospital. Every patient will be examined twice with a one-year interval (MR will only be repeated if clinically indicated).

Inclusion Criteria:

• Patients of any age with functionally single ventricle (patients under age 8 who need anesthesia for CMR will not be actively recruited. They may be approached to participate only if the anesthesia and CMR examination have been planned independently for clinical purposes)
• Written informed consent

Exclusion Criteria:

• Inability to follow the procedures of the study, e.g. due to language problems, psychological disorders, inability to give assent or consent, etc. of the participant and/or his/her parents or legal caregivers
• MR-incompatible implanted or accidentally incorporated metal device or claustrophobia that prohibits use of magnetic resonance imaging (patient and guardians fill out a questionnaire).
• Pregnancy
• Participation in another study is not an exclusion criterion, e.g. in a therapeutic trial.

Patients with single ventricle physiology