Cardiac output is the volume of blood pumped by the heart in one minute. It depends on two things. Heart rate is the number of beats each minute. Stroke volume is the volume of blood pumped out of a ventricle in one beat.
The equation is: cardiac output = stroke volume × heart rate. Stroke volume is measured in cm3, heart rate in beats per minute, and cardiac output in cm3 per minute.
Worked example: a heart has a stroke volume of 70 cm3 and beats 70 times each minute. Cardiac output = 70 × 70 = 4900 cm3 per minute.
The equation can be rearranged. Stroke volume = cardiac output divided by heart rate, and heart rate = cardiac output divided by stroke volume. For example, if the cardiac output is 6000 cm3 per minute and the heart rate is 80 beats per minute, the stroke volume is 6000 divided by 80 = 75 cm3.
During exercise the heart rate and the stroke volume both increase, so the cardiac output increases and more oxygen is delivered to the muscles.