one should consider if the catheter is within the coronary sinus Septum Primum and Patent Foramen Ovale The septum primum is used to move the catheter toward the limbus and test for presence or absence of a PFO Once the catheter is on the limbus, a clockwise rotation will often push the catheter through the PFO It is useful to check for the PFO because 15% to 25% of people have a patent foramen This access allows direct left atrial pressures and pulmonary vein saturations In addition, this access can allow the catheterization physician to perform a full diagnostic left heart cardiac catheterization through an existing atrial septal opening, thus precluding the need for an arterial sheath Transeptal Puncture Transeptal puncture is used in the absence of a PFO and in patients who need direct left atrial pressures and/or pulmonary vein saturations to best delineate the congenital heart anatomy and physiology Tricuspid Valve Apparatus Tricuspid Valve Atresia This single ventricle anatomy often does not often require cardiac catheterization unless there are anatomic considerations such as a restrictive atrial septum or concern for the restrictive nature of the pulmonary outflow anatomy from the LV across the VSD, or as a part of hemodynamic evaluation prior to the Fontan operation Tricuspid Valve Stenosis Pulmonary atresia intact ventricular septum patients have a small tricuspid valve apparatus and often warrant diagnostic evaluation with angiography of the RV (see pulmonary valve section) Ebstein Anomaly Ebstein anomaly is a rare congenital heart finding first described in 1866 by Ebstein, with the first surgical procedures in the late 1950s Diagnostic catheterization is at times necessary for evaluation of the tricuspid valve position, insufficiency, and filling pressures prior to surgical repair More often, the diagnostic catheterization is performed in adults after surgical repair of the tricuspid valve to assess hemodynamics and valve function, if this cannot be assessed by CMRI or echocardiography Right Ventricle and Right Ventricular Outflow Tract Saturations These saturations can be 3% to 4% lower than the RA, due to a low coronary sinus saturation (