In which congenital heart defect would you most likely observe early cyanosis?

Early cyanosis in congenital heart defects is typically associated with conditions that lead to right-to-left shunting of blood. In the case of truncus arteriosus, this defect involves a single large vessel arising from the heart that provides the systemic, pulmonary, and coronary circulation, rather than the normal separation into the aorta and pulmonary artery.

In truncus arteriosus, desaturated (or deoxygenated) blood mixes with oxygenated blood in the ventricle, which can then be delivered to the systemic circulation, leading to reduced oxygen delivery to tissues and resulting in cyanosis. This condition is characterized by the presence of a ventricular septal defect and is often accompanied by other anomalies, which complicates the typical blood flow patterns.

Other conditions such as ventricular septal defect, atrial septal defect, and coarctation of the aorta are more associated with left-to-right shunting or obstructive lesions that typically do not cause early cyanosis. In fact, many of these conditions may present without cyanosis in early life, particularly since blood oxygen levels can be adequate due to the functional nature of the left-to-right shunt.

Thus, truncus arteriosus is the correct answer because it leads to the mixing