This study will examine and record the patient's medical information and medical records (patient files, computer records, etc.). Physical examination, echocardiographic, electrocardiographic, laboratory, radiological, etc. evaluations are made during the routine controls of the patients. Within the scope of this study, no attempt will be made on the patients, no additional tests will be performed, or treatment changes will not be made in the patients because they are included in this study. After these records, KPET will be performed by a specialist doctor and physiotherapist for the patients who are directed to the Faculty of Physical Therapy and Rehabilitation Cardiopulmonary Rehabilitation Unit. Pulmonary function tests and respiratory muscle strength measurements will be performed on patients who have adequate rest after CPET.

Fontan Group Inclusion Criteria:

• Be between 8-55 years old
• Having undergone a Fontan operation
• Clinical stability of the patients (preserved ventricular function)
• No change in ongoing drug therapy that adversely affects clinical stability
• At least 1 year after the operation

Fontan Group Exclusion Criteria:

• Neurological and/or genetic musculoskeletal disease
• Having orthopedic and cognitive problems that prevent testing
• The patient's and/or family's unwillingness to participate in the study

Control Group Inclusion Criteria:

• Not have cardiovascular, neurological, and/or genetic musculoskeletal disease
• Not having orthopedic and cognitive problems that prevent testing
• The patient's and/or family's willingness to participate in the study

Patients aged 8-55 years who underwent the Fontan procedure and followed up by Department of Pediatric Cardiology will be included in the study. In the evaluation of patients in terms of suitability for the study, a detailed history, medical and family history, and a physical examination focused on all systems. The eligible patients will be referred to the Cardiopulmonary Rehabilitation Unit after the routine evaluations including demographic and clinical characteristics and laboratory tests are completed. For patients aged 8-17 years, the parental informed consent form for the research study and the child consent form for the research study will be carefully explained and included in the study after the parents and patients have read, understood, and accepted. For patients aged 18 years and older, the informed consent form for the research study will be carefully explained and will be included in the study after the patients have read, understood, and accepted.