The goal of this observational clinical study look at the safety and effectiveness of the Occlutech Atrial Flow Regulator in the treatment of patients with failing Fontan circulation. This study will consist of a case series of congenital patients with Fontan failure who have been treated with an Occlutech AFR under the FDA's Expanded Access process.

The scope of this study is to gain clinical experience on the Occlutech AFR in Fontan failure patients. Cases in this study will be evaluated to evaluate the safety and effectiveness of the device.

The objective of this study is to evaluate the Occlutech AFR with respect to device safety and shunt patency at 1 year. Shunt patency defined by persistent right to left shunt assessed by echocardiography at 1-year post-procedure.

The Occlutech AFR Fontan Study is a single arm, observational, multicenter clinical investigation of the Occlutech Atrial Flow Regulator investigational device.

This is a retrospective, non-interventional, observational study that utilizes existing clinical data previously collected during standard patient care. No new procedures or treatments will be administered as part of this study.

This study will comprise a case series of congenital patients with Fontan failure who have been treated with an Occlutech AFR. The scope of this study is to gain clinical experience on the Occlutech AFR in Fontan failure patients. Cases in this study will be assessed to evaluate the safety and effectiveness of the device in a real-life scenario.

Sites will be selected in the U.S. that had previously attempted expanded access cases with the Occlutech AFR for Fontan failure. Data will be collected retrospectively up to a site-specific cut-off date, which will be either the date of IRB submission or IRB approval, per site IRB policy. The requirement for informed consent and HIPAA authorization will be determined by each IRB in accordance with applicable policies; waivers may be obtained where permissible. It is anticipated that 7 sites will be initiated for the study, and data from approximately 25 patients will be included.

Data will be descriptively compared to those available in the literature describing interventions on Fontan to modulate fenestration size.

Inclusion Criteria:

• The patient has been treated with an AFR device (attempted or successful) for failing Fontan through the Expanded Access Program of the Food and Drug Administration (FDA).
• The candidate/candidate's legal guardian has been informed of the nature of the study, agrees to its provisions and has provided written informed consent unless the site's IRB provided a waiver of consent.

Exclusion Criteria:

• If a subject does not meet the eligibility criteria, they will be considered a Screen Failure and cannot be included

The study population will include participants with a dysfunctional Fontan circulation who can benefit from the creation, enlargement, or reduction of a fenestration to achieve tolerable systemic venous pressures.