cardiac output
Cardiac output is the heart's flow rate — how many liters of blood it delivers to the body every minute. Think of it as the heart's gallons-per-minute rating, the bottom line of how well the pump is supplying the tissues.
It is the product of two factors: stroke volume (blood per beat) times heart rate (beats per minute). A typical resting adult moves about 5 liters per minute, roughly the body's entire blood volume each minute; heavy exercise can raise this several-fold.
Because output equals stroke volume times rate, the heart can defend it in two ways. If stroke volume falls, a faster rate can keep output up — which is why a struggling heart often beats faster. But there are limits: extreme tachycardia shortens filling and can paradoxically lower output.
When cardiac output cannot meet the body's needs, organs are underperfused, producing fatigue, breathlessness, low blood pressure, and in severe cases shock. Restoring adequate output is a central goal in treating heart failure and circulatory collapse.
A stroke volume of 70 mL at a heart rate of 72 beats per minute gives a cardiac output of about 5 liters per minute — a normal resting value.
Multiply per-beat volume by beats per minute to get output per minute.
Cardiac output = stroke volume × heart rate. To compare hearts of different body sizes, clinicians often divide output by body surface area to get the cardiac index.