The rhythmic sounds of a beating heart are produced by blood flow and the function of its internal structures. These noises, audible through a stethoscope, provide a direct window into the heart’s mechanical health. The most recognizable of these are the “lub-dub” sounds that occur with every beat. Variations from the normal rhythm or the presence of extra noises can indicate different health states, from the benign to those requiring further investigation.
The Normal Lub-Dub
The classic “lub-dub” represents the two main heart sounds, known clinically as S1 and S2. These sounds are the result of heart valves snapping shut during the cardiac cycle. The initial “lub,” or S1, is generated by the closure of the mitral and tricuspid valves. These valves separate the heart’s upper chambers (atria) from its lower chambers (ventricles), and their closing marks the beginning of systole, when the ventricles contract to pump blood to the lungs and body.
Following the “lub,” the “dub,” or S2, is the sound of the aortic and pulmonic valves closing. These valves control blood flow out of the ventricles and into the major arteries. Their closure signals the end of ventricular contraction and the start of diastole, the period when the ventricles relax and refill with blood. The S2 sound is naturally split because the aortic valve closes just before the pulmonary valve, a difference that can sometimes be heard in younger individuals during inspiration.
Abnormal Heart Sounds
Beyond the standard S1 and S2, other sounds can occur, indicating changes in blood flow or heart structure. The most common are heart murmurs, often described as whooshing or swishing sounds caused by turbulent blood flow. This can happen when blood moves through a narrowed opening or flows backward through a leaky valve. Murmurs can be “innocent,” which are harmless and frequently heard in children or during pregnancy, or “pathological,” which point to an underlying cardiac issue.
Other abnormal sounds include gallops and clicks. A gallop involves extra heart sounds, labeled S3 and S4, creating a rhythm that resembles a galloping horse. An S3 sound occurs early in diastole and, in adults, can be a sign of heart failure, as it suggests the ventricles are struggling to receive incoming blood. An S4 sound happens just before the S1 “lub” and almost always signifies a problem, often related to a stiff ventricle. Clicks are short, high-pitched sounds that might indicate an issue like mitral valve prolapse.
Causes of Abnormal Sounds
Heart murmurs frequently arise from valvular heart disease. This can take the form of stenosis, where a valve becomes stiff and narrowed, forcing blood to squeeze through a smaller-than-normal opening. A murmur can also be caused by regurgitation, where a valve doesn’t close properly, allowing blood to leak backward into the chamber it just left.
Structural defects can also generate abnormal sounds. An atrial septal defect (ASD) or a ventricular septal defect (VSD), which are holes in the walls separating the heart’s chambers, can cause murmurs by allowing blood to flow through an abnormal pathway. Gallop rhythms are often associated with conditions that affect the heart muscle, such as cardiomyopathy. A weakened heart muscle may produce an S3 sound, while a thickened one can lead to an S4 gallop.
How Doctors Evaluate Heart Sounds
The primary method for evaluating heart sounds is auscultation, which is listening to the body’s internal sounds with a stethoscope. A physician will place the stethoscope at several specific locations on the chest, as each position is best for hearing a particular heart valve without interference from the others. During this examination, the doctor pays close attention to the timing, loudness, pitch, and quality of the sounds.
If an abnormal sound is detected during auscultation, it often prompts further testing to get a clearer picture of the heart’s condition. The most common next step is an echocardiogram. This non-invasive procedure uses ultrasound waves to create a moving image of the heart. An echocardiogram allows a doctor to visualize the heart’s chambers, valves, and blood flow, helping to identify the structural cause of an abnormal heart sound.