The heart produces sounds as it contracts and relaxes, moving blood through its four chambers and valves. The familiar “lub-dub” rhythm is composed of two distinct sounds, S1 and S2, which represent the closing of the heart’s valves. S1 (“lub”) signals the closure of the mitral and tricuspid valves at the beginning of ventricular contraction. S2 (“dub”) occurs when the aortic and pulmonary valves close as the ventricles relax. Abnormal heart sounds deviate from this typical sequence, often indicating turbulent blood flow or mechanical issues within the heart structure, requiring further investigation.
How Abnormal Heart Sounds Are Classified
Physicians classify abnormal heart sounds primarily by their timing within the cardiac cycle, referencing S1 and S2. Murmurs are the most common type, described as a whooshing, blowing, or rasping noise caused by turbulent blood flow. Systolic murmurs occur between S1 and S2, during the period when the ventricles are contracting and pushing blood out of the heart.
Diastolic murmurs occur after S2 and before the next S1, while the ventricles are relaxing and filling with blood. Since the heart is usually quieter during this filling phase, diastolic murmurs are often softer and indicate a more serious underlying problem. Murmurs are further characterized by their intensity, measured on a scale from one to six, as well as their pitch and location on the chest.
Gallops are another category, characterized by the addition of a third (S3) or fourth (S4) heart sound, creating a triple rhythm. The S3 sound, or ventricular gallop, occurs early in the diastolic phase and is often described as having a cadence similar to “Kentucky.” This low-pitched sound results from rapid ventricular filling when the chamber walls are stiff or overloaded.
The S4 sound, or atrial gallop, is a low-pitched sound occurring late in diastole, just before S1, often likened to the rhythm of “Tennessee.” It is produced when the atria contract forcefully to push blood into a stiff ventricle. Other distinct noises include sharp, high-pitched clicks occurring in systole, and opening snaps heard in early diastole.
A pericardial friction rub is a unique finding that sounds like a grating, scratching, or squeaking noise, often likened to leather rubbing against leather. This sound typically has three components corresponding to different phases of the cardiac cycle. The rub originates outside the heart muscle itself, differentiating it from murmurs and gallops generated by blood flow or muscle action.
Medical Conditions That Cause Abnormal Sounds
The structural integrity of the heart’s four valves is the most frequent source of murmurs. Valvular stenosis occurs when a valve’s leaflets become stiff or narrowed, impeding the forward flow of blood. This restricted opening forces blood through a smaller channel, creating the turbulent, whooshing sound as blood velocity increases.
Conversely, valvular regurgitation, or insufficiency, happens when a valve does not close completely, allowing blood to leak backward into the previous chamber. This backflow generates turbulence and is responsible for many murmurs. For example, a leaky mitral valve allows blood to flow back into the left atrium during ventricular contraction, causing a systolic murmur.
Abnormal heart sounds can also result from congenital defects, which are structural problems present from birth. Septal defects involve a hole in the wall separating the heart chambers, such such as an Atrial Septal Defect (ASD) or a Ventricular Septal Defect (VSD). These holes allow blood to shunt directly between the high-pressure and low-pressure sides of the heart, creating a loud, distinctive murmur due to mixing and turbulent flow.
Gallops (S3 and S4 sounds) are most often caused by changes in the heart muscle, particularly in the ventricles. Cardiomyopathy, a disease of the heart muscle, can cause the ventricular walls to become weak and dilated, leading to an S3 sound as blood rushes into the chamber. The S4 sound is associated with conditions like uncontrolled hypertension, where the left ventricle becomes abnormally thick and stiff, making it resistant to filling.
The pericardial friction rub is a direct result of inflammation of the pericardium, the thin, two-layered sac that surrounds the heart. In pericarditis, the inflamed layers of the sac rub against each other during the heart’s movement. This friction creates the characteristic grating sound, which is related to the mechanical movement of the irritated tissue surfaces rather than blood flow.
Confirming the Diagnosis
Once an abnormal sound is detected with a stethoscope, additional testing is necessary to determine the precise cause, severity, and extent of underlying damage. The echocardiogram, or “echo,” is the primary non-invasive tool used for this purpose. This ultrasound test uses sound waves to create moving pictures of the heart, allowing clinicians to visualize the heart’s structure and function in real-time.
An echocardiogram clearly shows how the heart valves are opening and closing, identifying whether a valve is stenotic (narrowed) or regurgitant (leaky). It also provides measurements of chamber size, wall thickness, and the efficiency of the heart’s pumping action, helping confirm conditions like cardiomyopathy or septal defects. Specialized techniques, such as Doppler flow imaging, measure the speed and direction of blood flow to quantify the turbulence causing the sound.
The electrocardiogram (EKG or ECG) is a simple test that records the heart’s electrical activity, providing a snapshot of its rhythm. While it cannot visualize structural problems, an EKG can reveal signs of heart strain, such as ventricular enlargement, which often accompanies significant valvular disease. It can also detect abnormal heart rhythms that may be a consequence of the underlying structural issue.
A Chest X-ray offers a broad view of the chest cavity and provides structural context for the diagnosis. It helps determine if the heart is enlarged, a common finding in conditions causing abnormal sounds, such as chronic valve disease or heart failure. The image can also show signs of fluid buildup in the lungs, known as pulmonary congestion, which may indicate compromised pumping ability.