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What Is Heart Murmur?

The heart, being a mechanical pump, is noisy. Normal heart sounds, the familiar two-part stroke sound of the heart “beat,” are due to the cardiac valves closing, easily heard in auscultation through a stethoscope.

There are two normal heart sounds, labeled S1 and S2, and extra heart sounds labeled S3 and S4. The clichéd “Lub-Dub” of the heartbeat heard through a stethoscope minimizes and understates the complexity of what actually is occurring.

The First Heart Sound

Designated S1, it represents the nearly simultaneous closure of the left and right atrioventricular valves (the mitral and tricuspid valves, respectively) and is created from reverberation within the blood as an effect of the sudden block of blood flow by the valves. Since it occurs first, it represents the beginning of atrial diastole and the initiation of ventricular systole. S1 is a confluence of two sounds, M1 and T1, i.e., mitral valve and tricuspid valve closure. The near simultaneity of M1 and T1 can separate in some heart blocks of conduction.

The Second Heart Sound

Designated S2, it represents the closure of the pulmonary and aortic valves and is created from reverberation within the blood as an effect of the sudden block of flow reversal. The S2 sounds–known as A2 and P2–take place at the end of ventricular systole and the beginning of ventricular diastole. With inspiration, the S2 sound’s A2 and P2 can separate, but a wide split indicates an arrhythmia.

  • Systole takes place between S1 and S2
  • Diastole takes place between S2 and the subsequent S1 of the next cycle

Other Sounds: S3 and S4–Ventricular Filling Sounds

S3 and S4 are low-frequency diastolic sounds that originate in the ventricles. S3 occurs at the beginning of diastole after S2, is lower in pitch than S1 or S2, is not of valvular origin, and is thought to be caused by the oscillation of blood back and forth between the walls of the ventricles initiated by blood rushing in from the atria. The S3 sound is indicative of increased volume of blood within the ventricle. An S3 is able to be distinguished as either left- or right-sided by whether or not it increases in intensity with inhalation or exhalation. A right-sided S3 will increase upon inhalation, and a left-sided S3 will increase with exhalation.

S4 occurs just after atrial contraction at the end of diastole and immediately before S1, and is caused by the result of blood being forced into a stiff or hypertrophic ventricle, so it indicates pathology such as hypertension, aortic stenosis, or cardiomyopathy. Gallops are abnormal S3 and S4 sounds, louder and higher pitched (sharper). S3 is the ventricular gallop and S4 is the atrial gallop sound.

Heart Murmurs

Murmurs are extra sounds heard as distinct from the S1 and S2 and are described in relation to the timing associated with both heart sounds. They are the result of turbulence of flow of blood (the sound is called a bruit) and are useful in diagnosing the valvular diseases that create them.

  • Systolic heart murmurs occur during systole: Between the S1 and S2 sounds
  • Diastolic murmurs occur during diastole: Between the S2 and the next S1

Significance of Heart Murmurs

Since the flow through the heart should be smoothly repetitive, any structural abnormalities will add noise to the auscultation due to turbulence and valve disease. Heart murmurs, therefore, are important diagnostic clues for heart and valvular disease identification which steers further diagnostics and subsequent therapies.


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This information is provided by Vascular Health Clinics and is not intended to replace the medical advice of your doctor or healthcare provider. Please consult your healthcare provider for advice about a specific medical condition.

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