A simplified model of the heart and circulation. Move the sliders to change heart rate and stroke volume, and watch the beat drive blood around the loop while cardiac output updates.
This is a simplified model of the left side of the heart and the loop it drives. Blood returns through the vena cava, fills the left ventricle, and is pumped out through the aorta to the capillaries, where the moving dashes show the flow.
Two numbers drive it all: the heart rate, how many beats per minute, and the stroke volume, how much blood leaves the ventricle in each beat. Their product is cardiac output, the volume pumped every minute.
At rest the heart is unhurried, and during exercise both the rate and the strength of each beat climb. By moving the sliders you can recreate that range and watch how the loop responds â faster beats and stronger beats both lift cardiac output.
The bar and the readouts show the result, and the organic state label changes from resting to light, moderate and intense activity as output rises.
Used blood flows back to the heart through the vena cava. In this model the returning flow is kept fairly steady, providing a continuous supply for the next beat.
While the heart rests between beats, the mitral valve opens and the left ventricle relaxes and expands to fill with blood. The model grows the ventricle at this point so the filling is visible.
The beat arrives: the ventricle squeezes smaller, the mitral valve shuts and the aortic valve opens, so blood is forced out into the aorta rather than back into the atrium.
Blood leaves through the aorta and travels to the capillary bed. The dashes speed up as a fresh pulse arrives and slow between beats, so the rhythm of the heart carries all the way around the loop.
Cardiac output equals stroke volume times heart rate. Raise either one and the output bar grows; lower them and it shrinks. The readout shows the value in litres per minute.
Cardiac output is the volume of blood the heart pumps each minute. It is simply stroke volume multiplied by heart rate, so both a faster beat and a bigger beat raise it. The model reads it in litres per minute.
Stroke volume is how much blood the left ventricle ejects in one beat, measured here in millilitres. At rest it is around 70 mL, and it rises during exercise as the heart contracts more strongly.
The ventricle relaxes and expands to fill with blood, then contracts and shrinks to push it out. The model shows that squeeze and release so you can see the pumping action of each beat.
The mitral and aortic valves act as one-way doors. The mitral valve opens to let the ventricle fill and shuts when it squeezes; the aortic valve opens to let blood out and shuts to stop it flowing back.
The dashes show the direction of flow along each vessel. They speed up when the heart pushes a fresh pulse out and slow between beats, so the rhythm of the beat travels through the circuit.
No. It is a heavily simplified teaching model with just two adjustable numbers, not a clinical tool. Real circulation depends on many more factors and cannot be judged from this diagram.