Abstract An understanding of the anatomy, physiology, and alternative treatment strategies for congenital heart defects is essential to provide the appropriate patient care This chapter reviews current indications and best practice guidelines by proceeding through the diagnostic cardiac catheterization procedure from beginning to end in the order of anatomic structures evaluated Keywords Cardiac Catheterization; Pediatric and Adult Congenital Diagnosis Introduction An understanding of the anatomy, physiology, and alternative treatment strategies for congenital heart defects is essential to provide the appropriate patient care This includes an understanding of the guideline recommendations and the natural history of congenital heart defects This knowledge is required to determine if there is an indication for treatment of these conditions Pediatric and adult congenital heart patients offer distinct challenges, such as unusual cardiovascular anatomy and deranged or surgically corrected physiology, and for older patients there are demands such as pregnancy and exercise tolerability not found in traditional patients Diagnostic cardiac catheterization for children with heart disease and adults with congenital heart disease is the practice of percutaneous catheter-based techniques to assess cardiovascular hemodynamics and anatomy Real-time fluoroscopy with contrast injection coupled with rapid digital angiography provides high-resolution images of the heart that are necessary for successful management decisions In addition, the direct measurement of pressures within the cardiovascular system enhances the treatment of heart disease for this patient population by streamlining medical treatment options and defining surgical and interventional indications This chapter reviews current indications and best practice guidelines by proceeding through the diagnostic cardiac catheterization procedure from beginning to end in the order of anatomic structures evaluated Historical Background In 1628 the court physician to James I and Charles I of England, Dr William Harvey, presented the “movement of the heart and blood” in an experiment on a deer He used his experiments and deductive logic to conclude that blood was pumped by the heart through systemic and pulmonary circulations These experiments confirmed unidirectional blood flow in the blood vessels In 1929 Werner Forssmann of Germany demonstrated on himself the ability to move a urethral catheter into his basilic vein in his left arm to his heart He then walked to radiology and made an x-ray to prove the catheter course After this report he was fired by his chief of surgery who said “for a real surgeon, there is only one thing, to operate, to operate, to operate.” Ultimately, he was awarded the Nobel Prize in 1956 Over the next 6 decades, the field of structural and congenital cardiac catheterization evolved into primarily an interventional discipline.1 Accordingly, diagnostic cardiac catheterization evolved to mostly the preintervention evaluation and assessment Meanwhile, the pure diagnostic cardiac catheterization regressed to a limited and select patient group Currently the diagnostic cardiac catheterization and percutaneous interventional procedures are not mutually exclusive It is currently recommended2,3 that percutaneous interventions are preceded by a diagnostic evaluation that most often determines the indications for that intervention (class I; level of evidence: A) Consequently, assessment of patient hemodynamics and, when necessary, assessment of anatomy by angiography should be accomplished before the interventional cardiac catheterization to confirm congenital or acquired heart disease in infants and children, as well as adults with congenital heart defects.4 On the other hand, most pure diagnostic cardiac catheterizations will often include preprocedure discussions regarding potential interventions if indications for an interventional procedure are met during the diagnostic evaluation Consequently, both the procedural preapproval process and the informed consent process for most diagnostic cardiac catheterizations include consent for any possible intervention This is essential in the management of children but even more so for older children and adults where assent and consent from the patient is mandatory prior to sedatives This preparation will allow congenital heart patients, who have often already undergone multiple procedures, to avoid more ... This knowledge is required to determine if there is an indication for treatment of these conditions Pediatric and adult congenital heart patients offer distinct challenges, such as unusual cardiovascular anatomy and deranged or surgically corrected physiology, and for