Final answer:
Infants increase their cardiac output primarily by increasing their heart rate or stroke volume or both.
Step-by-step explanation:
Infants increase their cardiac output primarily by increasing their heart rate or stroke volume or both. Cardiac output is the measurement of blood flow from the heart through the ventricles, and it is usually measured in liters per minute. Elevating heart rate or stroke volume or both will elevate blood pressure and promote blood flow. Factors that can increase cardiac output include sympathetic stimulation, the catecholamines epinephrine and norepinephrine, thyroid hormones, and increased calcium ion levels.