A little more
understanding.
Four chambers. Two connected circuits. Follow the flow through the extraordinary muscle working quietly inside you. The right side sends blood toward the lungs. The left sends it through the body. In this front-facing cutaway, anatomical right appears on your left.
How it works
The right side sends blood toward the lungs. The left sends it through the body. In this front-facing cutaway, anatomical right appears on your left. Select a chamber, valve group or electrical pathway. Cyan means lower oxygen and coral means oxygen-rich blood; blood is never actually blue. Change the illustrated heart rate or inspect filling and pumping. Pressure differences open and close valves to direct flow. Blood returning from the body enters the right atrium, travels through the right ventricle to the lungs, then returns to the left side before going back to the body. Heart rate multiplied by stroke volume gives cardiac output. The values here illustrate the calculation; they are not a measurement of your heart.
Dive deeper
Cardiac output and stroke volume
Stroke volume is the amount ejected by a ventricle per beat. Multiplying it by heart rate gives output per minute. In steady conditions the two sides have approximately matched output. Stroke volume does not stay fixed when heart rate changes; the calculator holds it constant only to illustrate the relationship.
Q = HR × SV = 75 beats/min × 70 mL/beat = 5.25 L/minPressure controls the valves
During filling, ventricular pressure is low relative to atrial pressure, allowing atrioventricular valves to open. Ventricular contraction raises pressure, closes those valves, then opens the outflow valves when pressure exceeds the pulmonary artery or aorta. Brief intervals exist when all valves are closed.
An electrical event is not a muscle contraction
Electrical activation precedes the mechanical response. The sinoatrial node, atrioventricular node and ventricular conduction system coordinate timing. The faint trace below the diagram is an illustrative motif, not a diagnostic ECG recording.
Interesting facts
4 — chambers. Two atria receive blood; two ventricles pump it onward.
2 — connected circulations. Pulmonary circulation and systemic circulation.
5.25 L — per minute, in this example. 75 beats/min × 70 mL/beat = 5,250 mL/min.
Good questions.
Is blood really blue before it reaches the lungs?
No. Human blood is red, with color varying by oxygenation. Cyan and coral are diagram colors chosen to help distinguish the two pathways.
Do all four chambers contract at the same moment?
No. The electrical conduction system coordinates atrial activation before ventricular activation. The ventricles pump together into separate circuits; the simplified filling and pumping control does not resolve every phase.
Can I use this to interpret my heart rate?
This exhibit teaches general anatomy and physiology. Its adjustable rate and output calculation are illustrative and do not assess an individual’s health or replace a clinical measurement.