Healthy Heart Sounds

When a heart is healthy, it makes a distinct "lub-dub" sound. When doctors begin a physical diagnosis and listen to the sounds made by a patient's heart, they are said to be performing auscultation. The two parts of that sound -- the "lub" and the "dub" -- speak volumes about how the valves within the heart (and the muscle itself) are functioning.

Heart Basics

• The human heart is a muscular pump, located behind the protective wall of the sternum and ribs. Adult hearts are about the size of a fist, but despite its small size the heart has the awesome responsibility of distributing blood throughout the body. The muscle of the heart is nestled in a liquid-filled sac called the pericardium, which protects it and allows it to beat smoothly within the close quarters of the chest.

Path of Blood

• The sounds we hear when we listen to the heart are made by the blood that moves through it. Large arteries deliver deoxygenated blood into the right side of the heart, which circulates the blood into the lungs to be filled with oxygen. Then it goes back to the left side of the heart, where the muscle delivers that newly oxygenated blood into the body. The valves that admit the blood through this system are all strictly one-way in a healthy body, sealing each part of the pathway as the blood passes through.

The "Lub-Dub" Sound

• The "lub-dub" sound that you hear when you listen to a healthy heart has two parts, called S1 and S2. They distinguish systole (the time when the heart is contracting) from diastole (the time when the heart is relaxing, or dilating). When the heart makes these sounds clearly and without any "extra" sounds, the heart is said to have a normal sinus rhythm (the regular rhythm set by the sinoatrial node, the heart's natural pacemaker).

Meaning of S1

• The first sound, or S1, is the heart sound we hear at the beginning of systole. The heart makes this sound when the pressure of the blood outside the heart during contraction is greater than the pressure inside the atrium (or heart chamber). his pressure differential causes the valves to close quickly.

Meaning of S2

• The ventricles (lower heart chambers) continue to contract during systole, which moves the blood through the valves. When the muscle begins to relax (during diastole) and the pressures inside the heart drop below those of the pressures in the aorta and the artery to the lungs, blood flows in to make the valves close again. When those valves close, we hear the second sound, or S2.