Your heart, beat by beat
Trace one heartbeat: from the pump itself to the vessels that carry blood around your body and back.
5 minutes · 6 stops
- A double pump
Your heart is two pumps working side by side. The right side sends blood to the lungs to collect oxygen. The left side, thicker and stronger, sends that fresh blood to the rest of you. It beats about 100,000 times a day without you ever thinking about it.
- Valves keep it one-way
Four valves open and snap shut with every beat so blood can only flow forward. The "lub-dub" you hear through a stethoscope is the sound of these valves closing. A valve that leaks or is too stiff makes an extra sound called a murmur.
- Feeding the heart itself
The heart muscle needs its own blood supply. The coronary arteries wrap around it like a crown. When one of them becomes blocked, part of the heart muscle is starved of oxygen, which is what happens in a heart attack.
- Out through the aorta
Each squeeze of the left ventricle pushes blood into the aorta, the body's main artery, which arches over the heart and runs down in front of the spine. Its stretchy wall swells with each beat and springs back, keeping blood moving even between beats.
- A pulse you can feel
Every heartbeat sends a pressure wave along your arteries. Press two fingers on the thumb side of your wrist and you can feel it in the radial artery. Counting it for 30 seconds and doubling the number gives your heart rate.
- Back to the heart
Used blood returns through veins. The two largest, the superior and inferior venae cavae, empty into the right side of the heart. From there it is pumped to the lungs to drop off carbon dioxide and pick up oxygen, and the cycle begins again.