A 2-year-old boy shows signs of failure to thrive with a specific cardiac murmur. What congenital anomaly is most likely present?

In this scenario, the presence of failure to thrive along with a specific cardiac murmur in a 2-year-old boy points towards a congenital heart defect that is commonly associated with such clinical findings. An atrial septal defect (ASD) is a condition where there is a hole in the wall (septum) separating the two upper chambers of the heart (the atria). This defect can lead to a left-to-right shunt, allowing oxygen-rich blood to flow into the right atrium and then the right ventricle, which can subsequently lead to increased blood flow to the lungs.

The additional blood flow can result in pulmonary overcirculation, which may manifest as failure to thrive due to the increased workload on the heart and lungs. Furthermore, children with ASD may be asymptomatic for a time but can develop signs of heart failure as the pulmonary circulation becomes overloaded.

The characteristic murmur associated with ASD is often a widely split second heart sound and a systolic ejection murmur due to increased flow across the pulmonary valve, making it identifiable during a physical examination.

Other congenital anomalies, such as patent ductus arteriosus, tetralogy of Fallot, and transposition of the great arteries, have different clinical presentations and would