The cardiac output (CO) is the volume of blood ejected by the heart each time it beats. It is the product of stroke volume (SV) and heart rate (HR) and is expressed in litres per minute. It gives a measure of the performance of the heart as a pump. The normal resting CO of a 70kg person is approximately 5 to 6 litres/min, due to a resting HR of 70-80 bpm multiplied by an average SV of 70-80ml. Different organs in the body receive differing proportions of the CO according to their demand. CO increases significantly in pregnancy due to the growing uterus, fetus and placenta, and its actual value can be affected by patient position and medical interventions, such as epidural analgesia.