Heart rate, stroke volume and cardiac output

Heart rate is the number of times the heart beats in one minute, measured in beats per minute (bpm). You can find it by taking a pulse for a set time and scaling up to one minute.

Stroke volume is the volume of blood pumped out of the heart in one beat, usually measured in cm³. Cardiac output is the volume of blood pumped by the heart in one minute, measured in cm³ per minute.

The equation is: cardiac output = stroke volume × heart rate. It can be rearranged: stroke volume = cardiac output ÷ heart rate, and heart rate = cardiac output ÷ stroke volume.

Worked example: a heart pumps 70 cm³ per beat at 75 bpm. Cardiac output = 70 × 75 = 5250 cm³ per minute. During exercise both heart rate and stroke volume rise, so cardiac output rises and more oxygen is delivered to the muscles.