The aim of this study is to investigate whether venous compression garments increase exercise stroke volume in patients with Fontan circulation. To address this aim, we will test the following hypotheses: 1. Acute and chronic external venous compression will increase exercise stroke volume in patients with Fontan circulation. 2. Patients with significant venous varicosities will have a greater response to venous compression. Participants will: * Undergo submaximal exercise testing in MRI to measure venous return and exercise stroke volume with and without the wearing of compression garments * Undergo submaximal exercise testing on a seated upright exercise ergometer with concurrent measurement of stroke volume with and without the wearing of compression garments * A subset of participants will repeat both testing visits after wearing compression garments for 2-weeks during waking hours. Participants will: * Undergo submaximal exercise testing in MRI to measure venous return and exercise stroke volume with and without the wearing of compression garments * Undergo submaximal exercise testing on a seated upright exercise ergometer with concurrent measurement of stroke volume with and without the wearing of compression garments * A subset of participants will repeat both testing visits after wearing compression garments for 2-weeks during waking hours.
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Change in Stroke Volume with Exercise
Timeframe: Rest (20 minutes), Exercise (10 minutes)
Change in Stroke Volume with Exercise
Timeframe: Rest (20 minutes), Exercise (10 minutes)
Change in Stroke Volume with Exercise
Timeframe: Rest (20 minutes), Exercise (10 minutes) at 2-weeks follow-up testing
The Acute Effect of Compression Garments on Stroke Volume during Exercise
Timeframe: Rest (20 minutes) and Exercise (10 minutes) repeated during baseline testing
The Chronic Effect of Compression Garments on Stroke Volume during exercise
Timeframe: Rest (20 minutes) and Exercise (10 minutes) completed during baseline and during follow-up testing