How many nuclei does a typical cardiac myocyte have?

• A. Many
• B. Two
• C. None
• D. One

Answer: (D)

Cardiac myocytes are long-lived cells that grow mainly by increasing in size rather than by making more cells. Because they exit the cell cycle after birth, the heart adds tissue through hypertrophy, not through cell division. This leaves most adult cardiomyocytes with a single nucleus. Some cells can become binucleated under certain conditions, but that is not the common state in a typical healthy adult heart. Therefore, the usual number of nuclei in a cardiac myocyte is one.