What Are Heart Murmurs? Characteristics and Types

Heart murmurs are defined as the sound produced by the blood flowing through the valves of the heart. Discover the characteristics and types.
What Are Heart Murmurs? Characteristics and Types

Last update: 27 December, 2022

Cardiologists define heart murmurs as “the sound that blood makes as it passes through the heart valves.” They’re very common, so much so that up to 72% of children and adolescents are estimated to have a heart murmur at some point in their development. Most cases are benign, although sometimes they can be a symptom of a greater complication.

Most of the time, heart murmurs aren’t accompanied by symptoms, so almost all patients who have one are unaware of it. They’re diagnosed by chance on medical auscultation and, if they’re benign, they don’t require treatment. In the following paragraphs, we’ll show you the characteristics of heart murmurs and the ways in which they can appear.

The characteristics of heart murmurs

The heart’s made up of four chambers or compartments with their respective valves that regulate the amount of blood that enters and leaves each of them. The upper chambers are called atria (right and left) and the lower ones are called ventricles (right and left).

The valves that communicate the atria with the ventricles are called atrioventricular valves (the left is the mitral valve and the right is the tricuspid valve). Those that communicate the ventricles with the great blood vessels are the aortic valve (left) and pulmonary valve (right). These structures not only have the function of directing blood from one chamber to another but also preventing blood from returning.

When listened to with a stethoscope, a healthy heart produces a sound that doctors define as a lub-dub. Lub is the sound resulting from the contraction of the heart (systole) and the closure of the mitral and tricuspid valves. Dub is the sound resulting from the relaxation of the heart (diastole) and the closure of the aortic and pulmonary valves.

In this regard, a heart murmur is an additional sound to this regular lub-dub cadence. It’s characterized by a clicking, hissing, or humming sound that’s triggered by turbulent flow through the valves. This is the case most of the time, as the mechanical operation of the valves or the heart also causes its appearance.

The main causes of heart murmurs

A doctor listening to a toddler's heart.
Murmurs are frequently detected in children. These have certain characteristics that make them benign.

The Heart Foundation summarizes some of the main causes of heart murmurs:

  • Turbulent blood flow
  • Stiffness or numbness of the valves (a natural product of aging)
  • Valve stenosis
  • Infections in the valves of the heart
  • Side effects of rheumatic fever
  • Heart attack
  • Extreme exercise
  • Pregnancy
  • Overactivity of the thyroid gland
  • Anemia
  • Fast growth
  • Congenital heart conditions

Almost all heart murmur episodes can be explained on the basis of these mediators. As researchers point out, heart murmurs are very common in otherwise healthy infants, children, and adolescents, and most of these cases can be described as an innocent murmurs or a functional murmurs.

It’s estimated that less than 1% of heart murmurs in these groups are pathological. Therefore, they’re a benign condition that usually resolves in youth.

Murmurs usually occur without symptoms, although sometimes people may develop chest pain, rapid heartbeat (tachycardia), shortness of breath, and fatigue.

When these signs occur, they usually do so with a mild intensity, although they can cause anguish or anxiety in the patient. Murmurs can be diagnosed upon routine auscultation, and their volume, rhythm, and pitch vary depending on the type.

Types of heart murmurs

As Johns Hopkins Medicine rightly points out, heart murmurs are classified by their location, intensity, pitch, profile, and timing. The most important criteria are intensity and timing. Experts classify murmurs by intensity on a scale from 1 to 6. Let’s see exactly how they’re distributed by intensity:

  • Grade I: Very weak murmur, barely audible.
  • Grade II: Soft murmur.
  • Grade III: Easily audible, but with no palpable thrill.
  • Grade IV: Easily audible with a palpable thrill.
  • Grade V: A strong murmur, audible with a stethoscope lightly touching the chest.
  • Grade VI: A louder murmur, audible with a stethoscope without touching the chest.

The synchronization criterion has to do with the moment in which the murmur takes place. This is, as we’ve already seen, during systole or diastole. In this regard, there are three types of heart murmurs.

Systolic murmur

Experts classify a systolic murmur as a murmur or wheeze that begins during or after the first heart sound (lub) and ends before or during the second heart sound (dub). Two subtypes exist, namely, systolic ejection murmurs and systolic regurgitation murmurs.

In the first case, it occurs due to a narrow vessel or an irregularity in the heart valves. In the second case, it’s accompanied by a flow that goes back to one of the chambers of the heart.

Diastolic murmur

A specialist performing an echocardiogram.
The presence of a diastolic murmur is almost always abnormal. This requires determining the cause of the alteration through various methods, such as echocardiography.

Specialists classify diastolic murmurs as a murmur or wheezing that begins with the aortic component of the second sound (dub) and decreases in intensity during a variable duration of diastole. There are four main subtypes of this murmur, namely, aortic valve regurgitation, pulmonic valve regurgitation, mitral valve rumbling, and tricuspid valve rumbling.

All diastolic murmurs are related to an alteration of the cardiovascular structures. Compared to systolic murmurs, they’re more difficult to identify, so they require some experience or certain auscultation techniques. In short, this type of murmur occurs during the relaxation of the cardiac muscle.

Continuous heart murmurs

There’s a third category of heart murmurs called continuous murmurs. That is, murmurs that occur both during muscle contraction (systole) and during relaxation (diastole). They’re less common than the previous types, murmurs are usually synchronized at a specific moment of cardiac function.

As the intensity and synchronization of a murmur can hinder its detection, there are maneuvers that allow it to be enhanced. The most used are the isometric handgrip, squats, Valsalva, standing up quickly, and amyl nitrate. Patients who manifest symptoms often require imaging tests (echocardiogram) to rule out abnormalities in the heart.

If you have a heart murmur, your doctor will surely have given you words of comfort. Unless otherwise indicated, you can lead a normal life. Murmurs are mostly benign and don’t usually alter a person’s well-being. If you detect a worsening of symptoms, don’t hesitate to see your doctor for a more in-depth analysis.

  • Alpert, M. A. Systolic murmurs. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. 1990.
  • Crawley, I. S. Diastolic murmurs. 2011.
  • Doshi AR. Innocent Heart Murmur. Cureus. 2018;10(12):e3689. Published 2018 Dec 5.
  • Frank JE, Jacobe KM. Evaluation and management of heart murmurs in children. Am Fam Physician. 2011 Oct 1;84(7):793-800.
  • Mejia, E., & Dhuper, S. Innocent Murmur. In StatPearls [Internet]. StatPearls Publishing. 2020.
  • Thomas, S. L., Heaton, J., & Makaryus, A. N. Physiology, cardiovascular murmurs. In StatPearls [Internet]. StatPearls Publishing. 2021.

Este texto se ofrece únicamente con propósitos informativos y no reemplaza la consulta con un profesional. Ante dudas, consulta a tu especialista.