Following orthoptopic heart transplantation (OHT), children undergo surveillance cardiac catheterizations to assess for signs of rejection including muscle biopsy as well as pressure measurements. These procedures are done under general anesthesia which promotes lung tissue collapse (atelectasis). Atalectaisis is known to alter intra-thoracic pressures and cardiac loading conditions. What is not known is the effect of atelectasis on intracardiac pressures which are a critical area of monitoring post-transplant patients for rejection. Therefore, the aim of this study is to identify if atelectasis impacts the pressure measurements obtained during cardiac catheterization.