Which complication requires immediate reporting during the cardiac assessment of a newborn?

In the context of a cardiac assessment for a newborn, cool extremities with diminished pulses is particularly concerning. This finding indicates that there may be poor perfusion, which can be a sign of significant cardiac or circulatory issues, such as shock or heart failure. Diminished pulses suggest that the blood flow is compromised, which can lead to inadequate oxygen delivery to the tissues. Immediate reporting of this condition is critical to allow for prompt evaluation and intervention, thereby preventing further deterioration in the newborn's condition.

Normal heart sounds do not indicate any immediate problems that require reporting, and muffled heart sounds could suggest pericardial effusion, which may also require attention, but not as urgently as diminished pulses. Cool extremities with full pulses may indicate peripheral vasoconstriction without significant circulatory failure, hence they are less alarming than the scenario where pulses are diminished. Thus, the presence of cool extremities with diminished pulses calls for urgent attention in managing the newborn's health status.