Normal Pediatric Cardiac Anatomy, Physiology, and Embryology
The segmental approach
Describe every heart in three steps. First, atrial situs: solitus, inversus, or ambiguous, decided by the morphologic right atrium with its broad appendage, crista terminalis, and IVC connection. Second, ventricular loop: the morphologic right ventricle is identified by coarse trabeculation, a moderator band, and a more apically inserted septal leaflet of its AV valve; the left ventricle is smooth-walled with paired papillary muscles. Third, connections: AV concordance or discordance, ventriculoarterial concordance or discordance, and the great-vessel relationship (normally the pulmonary artery is anterior and to the left of the aorta). Coronary anatomy completes the description.
Fetal and transitional physiology
Fetal circulation relies on three shunts: ductus venosus, foramen ovale (right-to-left streaming from the IVC), and ductus arteriosus. Pulmonary blood flow is low because pulmonary vascular resistance (PVR) is high. At birth, lung expansion and rising oxygen tension drop PVR; the ductus closes functionally within days. PVR reaches near-adult levels over roughly six to eight weeks - which is exactly why a large unrestrictive VSD may not murmur or cause failure until weeks 4 to 8.
Normal values and maturation
Neonatal valve velocities are higher than adult values (pulmonary peak often 0.7–1.2 m/s, aortic up to about 1.5 m/s). Mitral inflow in the first days shows E less than A from delayed relaxation, reversing to E greater than A within the first year. Chamber sizes and coronary dimensions must be indexed as z-scores for body surface area, not compared with adult cutoffs.
Trap: right-axis and right-ventricle dominance are normal in a newborn; do not call them abnormal.