Cardiac pacemaker discharge at about 40-60 beats per minute, and are called the "secondary pacemaker". Further down the electrical conducting system of the heart is the Bundle of His. The left and right branches of this bundle, and the Purkinje fibres, will also produce a spontaneous action potential at a rate of 30-40 beats per minute, so if the SA and AV node both fail to function, these cells can become pacemakers. It is important to realize that these cells will be initiating action potentials and contraction at a much lower rate than the primary or secondary pacemaker cells. The SA node
Cardiac output cycle that delivers oxygen, nutrients and chemicals to the body's cells and removes cellular waste. Because it pumps out whatever blood comes back into it from the venous system, the quantity of blood returning to the heart effectively determines the quantity of blood the heart pumps out – its cardiac output, "Q". Cardiac output is classically defined alongside stroke volume (SV) and the heart rate (HR) as: In standardizing what CO values are considered to be within normal range independent of the size of the subject's body, the accepted convention is to further index equation () using Body surface area