Tachycardia in an infant between birth and age 1 month is a heart rate:

Rationale: A. A heart rate of 90–110 beats per minute is below the normal range for a newborn and would be considered bradycardia. B. 115–140 beats per minute falls within the normal resting range for infants, especially when asleep. C. 150–170 beats per minute can be normal during activity or crying in a newborn. D. Tachycardia in infants younger than 1 month is defined as a heart rate greater than 180 beats per minute at rest. Persistent tachycardia may indicate underlying conditions such as infection, dehydration, anemia, or cardiac disorders and warrants further evaluation.