How the heart pumps blood

Two circuits

The right side sends blood to the lungs. There it picks up oxygen and gives up carbon dioxide. The left side receives that blood and pumps it out through the aorta to the rest of the body. The two circuits run at the same time.

A heartbeat has two sounds, often described as lub-dub. They are the valves closing, not the muscle itself. The pulse you feel at the wrist is the pressure wave from the left ventricle, travelling through the arteries.

A beat you can feel

Arteries carry blood away from the heart, usually rich in oxygen. Veins carry it back. Capillaries, the tiny vessels between them, are where oxygen and nutrients actually pass into the tissues.

None of this is a promise about fitness or illness. It is the layout of the pump. A doctor, not a paragraph, is the person to ask about symptoms.

Two circuits

The heart is a muscular pump with four rooms. Valves keep the blood moving one way. The heart sits slightly left of centre in the chest, behind the breastbone. It is mostly muscle.

Put those two statements side by side. The first sets the condition. The second says what happens once that condition is met. How the heart pumps blood needs both. Drop the first and the second has nothing to explain. Drop the second and the first is only the scene.

A beat you can feel

It is mostly muscle. That muscle squeezes without you deciding to, for as long as you live.

The order is the explanation. What the first sentence names has to be there before the result in the second sentence can show up. The piece does not ask you to accept the result first and hunt for a cause afterwards.

A check you can make

That muscle squeezes without you deciding to, for as long as you live. There are four chambers.

A fair check is sequential. Confirm the first statement. Then see whether the second is the result of it, rather than a separate fact parked in the same piece. If the result shows up without the condition, this account does not cover what you are looking at.

The limit of the claim

There are four chambers. The two upper ones, the atria, receive blood.

The two statements do different jobs. One says what is there, what it is made of, or what acts on it. The other says the change that follows. The title names the change. It is not an inventory of parts.