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(5) Heart Attack and Cardiac Disorders

What are normal heart sounds?

During the mechanical events of the heart, the closing of various heart valves creates two distinct heart sounds.

You can readily hear the heart sounds through a stethoscope. When the two ventricles begin to contract, the mitral and tricuspid valves close abruptly. Then, the pulmonic and aortic valves open, and the leaves of these two valves vibrate from the sudden rise of pressure caused by the blood forcing them to expand.

The heart sound created primarily by the closing mitral and tricuspid valves is called the first heart sound, and it is often expressed as “lub” if you imitated the entire heart sounds as “lub-dub.” Soon after the first heart sound fades away, the pressure within the ventricles falls low enough for the aortic and pulmonic valves to close, and the mitral and tricuspid valves open.

The heart sound caused primarily by the closure of the pulmonic and aortic valves is called the second heart sound. Often, it’s expressed as a “dub” if you imitated the heart sounds. Because the expansion time of the ventricle’s contraction period (the diastole) lasts longer than the contraction period of the ventricles (the systole), there is a silence between each heart cycle. Consequently, the normal heart sounds can be expressed as lub-dub . . . silence . . . lub-dub . . . silence . . . and so on.

Occasionally, vibrations of the ventricular wall can be heard as the ventricles fill with blood pouring from the atria during the expansion period (diastole) of the ventricles. This heart sound is called the third heart sound, relatively common among healthy young people.

Various heart diseases produce abnormal heart sounds in terms of timing and intensity. The abnormal noise created by a damaged or diseased heart valve is termed heart murmur, and various heart diseases can cause different types of heart murmurs. You can hear very loud heart murmurs even without using a stethoscope.

Terms:

Diastole - expansion period of the ventricles.

Systole - contraction (pumping) period of the ventricles.

Heart murmur - abnormal noise generated by blood flow through a damaged heart valve or a congenital heart defect.

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