framework can be used to assist in forming a differential diagnosis, instituting therapy, and communicating with the pediatric cardiologist This approach encourages the provider to categorize patients into groups according to their age, presenting vital signs, and predominant symptoms Presentation of CHD often occurs at the time of transition from fetal to postnatal circulation The adaptation to extrauterine life involves closure of three shunts: the ductus arteriosus (DA), patent foramen ovale in the atrial septum, and ductus venosus Pulmonary vascular resistance (PVR) drops dramatically with the first breath and continues to diminish significantly over the next months It follows that closure of the DA and fall in PVR may cause infants with cardiac malformations to become symptomatic Timing of presentation correlates with these significant physiologic events Structural CHD can be divided into four major categories Each of the four categories has typical presenting symptoms due to the underlying hemodynamics The key to diagnosis is associating presenting symptoms and physical findings with each of the major categories of CHD The four categories of structural CHD are: (1) ductal dependent lesions that require a patent ductus arteriosus (PDA) for PBF; (2) ductal dependent lesions that require a PDA for systemic blood flow; (3) shunt lesions with right-to-left flow; and (4) shunt lesions with left-to-right flow ( Tables 86.1 and 86.2 )