The control group consisted of 18 healthy children. These children underwent cardiopulmonary testing, spirometry, chest ultrasound to assess the diaphragm, 6-minute walk test, respiratory muscle strength and quality of life. These tests were performed to assess the results of these tests in patients without previous illnesses.

The Fonta training group consisted of 14 children in the late postoperative period of Fontan surgery. These children underwent cardiopulmonary testing, spirometry, chest ultrasound to assess the diaphragm, 6-minute walk test, respiratory muscle strength and quality of life. These tests were performed at the initial stage and after two months of inspiratory muscle training to assess the results of these in postoperative patients and what changes the training could bring. The training was performed with the Power Breath device, the carda was quantified at 40% of the force exerted at maximum inspiratory pressure by manovacuometry. The patient was asked to perform 3 sets of 20 repetitions twice over the course of 7 days of the week. Monitoring was done in person and virtually, and the carda was increased according to the evaluator's perception of the ease of the exercise or if the patient reported it to be easy. The training lasted 2 months.

The Fonta Control Group consisted of 13 children in the late postoperative period of Fontan surgery. These children underwent cardiopulmonary testing, spirometry, chest ultrasound to assess the diaphragm, 6-minute walk test, respiratory muscle strength and quality of life. These tests were performed at the initial stage and after two months to assess the results of these tests in postoperative patients and whether there was any normal behavior.

The Fonta training group consisted of 14 children in the late postoperative period of Fontan surgery. These children underwent cardiopulmonary testing, spirometry, chest ultrasound to assess the diaphragm, 6-minute walk test, respiratory muscle strength and quality of life. These tests were performed at the initial stage and after two months of inspiratory muscle training to assess the results of these in postoperative patients and what changes the training could bring. The training was performed with the Power Breath device, the carda was quantified at 40% of the force exerted at maximum inspiratory pressure by manovacuometry. The patient was asked to perform 3 sets of 20 repetitions twice over the course of 7 days of the week. Monitoring was done in person and virtually, and the carda was increased according to the evaluator's perception of the ease of the exercise or if the patient reported it to be easy. The training lasted 2 months.

The mobility and thickness of the diaphragm muscle were assessed using ultrasound in M mode. Both variables were analyzed during spontaneous, relaxed breathing in terms of both tidal volume and deep breathing at vital capacity. Muscle mobility was examined along the right and left mid-axillary and parasternal lines with volunteers in both the supine and sitting positions. Muscle thickness was measured while the patients were in the supine position along the mid-axillary lines during both natural, relaxed and deep breathing. Measurements were taken in centimeters, with the largest value selected from at least three reproducible measurements.

Respiratory muscle strength was measured using maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP) with a digital manometer calibrated beforehand. The MIP was determined by the maximal inspiratory effort from the residual volume (RV), and the MEP was determined by the maximal expiratory effort from the total lung capacity (TLC). At least three reproducible maneuvers were performed, with the largest value used unless it did not exceed the previous value by more than 20%.