Acyanotic Heart Defects

The child isn't blue, so parents assume the heart is fine — but left-to-right shunting silently floods the lungs and can cause irreversible damage before symptoms become obvious.

Acyanotic heart defects shunt oxygenated blood from the left side of the heart back to the right side (left-to-right shunt), increasing pulmonary blood flow without initially causing cyanosis. The four high-yield defects are VSD (most common congenital heart defect), ASD, PDA, and coarctation of the aorta. VSD, ASD, and PDA all overload the pulmonary vasculature — the child presents with tachypnea, poor feeding, diaphoresis during feeds, frequent respiratory infections, and failure to thrive. A harsh holosystolic murmur at the left lower sternal border suggests VSD; a fixed split S2 suggests ASD; a continuous "machinery" murmur suggests PDA. Coarctation is the outlier — it narrows the aorta, creating a blood pressure discrepancy: higher in the upper extremities, lower or absent pulses in the lower extremities. A BP difference of >20 mmHg between arms and legs is a red flag. Over time, uncorrected left-to-right shunts cause pulmonary hypertension and can eventually reverse to right-to-left shunting (Eisenmenger syndrome), at which point cyanosis appears and the defect becomes inoperable.

Key Distinctions

Don't confuse acyanotic (left-to-right shunt, increased pulmonary flow, pink child) with cyanotic defects (right-to-left shunt, often decreased pulmonary flow, blue child). Students mix up PDA's machinery murmur with VSD's holosystolic murmur — location and quality differ. Coarctation doesn't involve a shunt at all; its hallmark is differential blood pressures, not a volume-overloaded lung.

Clinical Pearl

Think "L" for acyanotic: Left-to-right shunt, Lungs get flooded, child Looks pink but Labors to breathe. Four limb blood pressures catch coarctation.