The purpose of this study is to assess for acute hemodynamic changes after implementation of noninvasive negative pressure ventilation (as compared with spontaneous respiration) in pediatric patients with Fontan failure using modern negative pressure ventilators

Inclusion Criteria:

1. Patients with Fontan physiology with clinical evidence of Fontan failure as defined by those with one of the following in addition to Fontan circulation: New York Heart Association Class II, fluid retention, cyanosis, protein losing enteropathy, renal/hepatic dysfunction and/or subjectively qualify for hemodynamic assessment (by primary cardiologist).

Exclusion Criteria:

1. Patients which will likely require intubation for catheterization
2. Severely depressed systemic ventricular systolic function
3. Baseline airway obstruction
4. Plastic bronchitis
5. Significant OUTFLOW obstruction