What is the size of an infant's heart?

The size of an infant's heart is comparable to that of a fist. This analogy holds true as the heart's size can be somewhat proportional to the size of the individual's fist as they grow. For infants, their physiological development reflects smaller proportions, so the heart maintains a size that is smaller than that of larger children or adults, making the fist comparison appropriate.

The other options provide comparisons that do not accurately represent the heart’s size in infants. Any fruit or vegetable larger than a fist, like a grapefruit or a carrot, would not be representative of an infant's heart, which emphasizes the importance of understanding size relationships in anatomy. The peach is also larger than a fist, making it an unsuitable comparison for the size of an infant's heart.