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Four Doors, One Job: How Heart Valves Work

Before anything can go wrong, you need to see what right looks like. Meet the four valves, the two ways they can fail, and the two words — stenosis and regurgitation — that organise the whole topic.

Valves are one-way doors

The heart is a pump, and like any good pump it needs valves that let blood move in one direction only. There are four of them, and each sits at a doorway between two chambers, or between a chamber and the great artery leaving it. On the right side, the tricuspid valve guards the door from the right atrium into the right ventricle, and the pulmonary valve guards the exit into the lungs. On the left side — the higher-pressure side — the mitral valve guards the door from the left atrium into the left ventricle, and the aortic valve guards the exit into the aorta.

A healthy valve does two things perfectly. When blood should flow forward, it opens wide and out of the way, offering almost no resistance. When blood would flow backward, it snaps shut and seals tight, so not a drop leaks back. The closing is what you hear: the first heart sound (“lub”) is the mitral and tricuspid valves slamming shut as the ventricles squeeze, and the second heart sound (“dub”) is the aortic and pulmonary valves closing as the ventricles relax.

Two ways a door can fail

Almost everything in valvular heart disease comes down to one of two failures, and it helps to picture them as a real door. Stenosis means the door has become stiff and narrow — it no longer opens fully, so the heart has to push hard to force blood through a small gap. Regurgitation (also called insufficiency or “a leaky valve”) means the door no longer seals — it stays partly open when it should be shut, so blood sloshes backward with each beat.

These two failures stress the heart in very different ways, and that difference is the key to the whole topic. A stenotic valve forces the chamber upstream of it to generate extra pressure — a pressure load. A regurgitant valve forces that chamber to handle extra volume, pumping the same blood twice — a volume load. The heart adapts to each over years, which is why valve disease can be silent for a long time before symptoms appear. We will trace exactly how, valve by valve, in the guides that follow.

  1. Name the valve and the direction blood should flow through it.
  2. Ask: is the problem opening (stenosis) or closing (regurgitation)?
  3. Stenosis → pressure load on the chamber behind it. Regurgitation → volume load.
  4. Predict which chamber gets thicker (pressure) or bigger (volume) over time.