Mitral and Tricuspid valves snap shut ( LUB ). Blood is ejected to the lungs and body.
Here's a brief explanation:
The next time you hear your own pulse in a quiet room or watch a medical drama on TV, remember: You aren’t hearing the heart "beating." You are hearing the precise, split-second timing of four valves closing in perfect sequence—a mechanical symphony that keeps you alive.
The second heart sound, known as , is the "dub." It is shorter, sharper, and higher-pitched than the first sound.
The human heart is often compared to a tirelessly working pump, but it is perhaps better described as a rhythmic percussion instrument. Every minute of every day, it produces a signature "lub-dub" sound that clinicians use as a primary indicator of cardiovascular health.
If the valves don’t close properly or are stiff, the laminar (smooth) flow of blood becomes turbulent. That turbulence creates a heart murmur .
If a valve doesn't close all the way, blood leaks backward, causing a murmur.
Aortic and Pulmonary valves snap shut ( DUB ). Cycle repeats.
The first heart sound, medically referred to as , is the "lub." It is typically lower-pitched and slightly longer in duration than the second sound.
The "dub" occurs at the beginning of —the phase where the ventricles relax to refill with blood. Once the ventricles have finished pumping blood into the aorta and the pulmonary artery, the pressure in those major vessels becomes higher than the pressure inside the relaxing ventricles. To prevent blood from falling back into the heart, two more valves snap shut: The Aortic Valve: Leading to the rest of the body. The Pulmonary Valve: Leading to the lungs.
Valves closing silently would be ideal for efficiency, but the human body is a fluid system. When flaps of tissue snap shut, they vibrate. That vibration travels through the blood and chest wall, becoming the sound we hear.
