The following is found during the assessment of a 1-month-old infant. Which of the following would lead the nurse to suspect a cardiac defect?

A. Weight gain is typically a sign of adequate nutrition and growth, not a concern for a cardiac defect. B. Hyperactivity is not characteristic of infants, especially at 1 month of age, and is not a common sign of a cardiac issue in this age group. C. Pink mucous membranes indicate adequate oxygenation, which does not suggest a cardiac defect. D. Poor nutritional intake in an infant may signal an underlying cardiac defect, particularly if accompanied by fatigue with feeding, diaphoresis, or failure to thrive. Infants with congenital heart defects often have difficulty feeding due to increased energy expenditure and reduced oxygenation, making this a key red flag.