The heart produces rhythmic sounds as it pumps blood, offering insights into its health. While the familiar “lub-dub” sounds (S1 and S2) indicate normal valve closure, additional sounds can provide further clues. This article explores the S3 heart sound, its origin, and what its presence might signify.
The Basics of Heart Sounds
The “lub-dub” cadence of a heartbeat consists of two primary sounds: S1 and S2. S1, the “lub,” occurs when the mitral and tricuspid valves close at the beginning of ventricular contraction. This prevents blood from flowing backward into the atria as ventricles pump it forward. S1 is typically heard best at the heart’s apex.
S2, the “dub,” signals the closure of the aortic and pulmonic valves, marking the end of ventricular contraction and beginning of relaxation. This prevents blood from flowing back into the ventricles from major arteries. S2 is generally loudest at the heart’s base. These two sounds reflect the coordinated opening and closing of the heart’s four valves.
What Exactly is the S3 Heart Sound?
The S3 heart sound is an extra, low-pitched sound occurring shortly after S2 during diastole, the heart’s relaxation phase. It is also called a “ventricular gallop” or “protodiastolic gallop,” as its rhythm can resemble “Kentucky” (with the “Y” being S3). This sound typically appears about 0.12 to 0.18 seconds after S2.
The S3 sound arises from the rapid deceleration of blood rushing into a ventricle during early diastole. As ventricles relax and fill, blood flows quickly from the atria. If the ventricle is stiff or overly compliant, this rapid inflow causes vibrations in the ventricular walls and chordae tendineae, creating the audible S3 sound.
When an S3 Sound is Normal
An S3 heart sound is not always a problem; it can be a normal, or “physiological,” finding. This physiological S3 is commonly heard in children and young adults, typically under 40. Their hearts are often highly compliant and fill rapidly, naturally producing the sound without underlying heart disease.
The S3 sound can also be present in other healthy conditions with increased blood volume returning to the heart. Pregnant individuals, for instance, may exhibit an S3 due to increased blood volume during gestation. Highly trained athletes can also have a physiological S3, as their larger hearts pump more efficiently, leading to increased stroke volume and rapid ventricular filling.
When an S3 Sound Indicates a Problem
When an S3 heart sound is heard in individuals over 40, or outside physiological categories, it typically indicates an underlying cardiac issue. This “pathological” S3 is commonly associated with heart failure. Here, the S3 suggests the ventricle cannot effectively handle blood volume, often due to impaired pumping or volume overload.
A pathological S3 can point to conditions like systolic heart failure, where pumping chambers struggle to eject blood efficiently. It can also be found in severe mitral or tricuspid regurgitation, where leaking heart valves cause blood to flow backward, increasing ventricular volume load. Other causes may include chronic severe anemia or high-output states, where the heart works harder, leading to increased ventricular blood flow.
How S3 is Detected and Evaluated
Healthcare professionals typically detect an S3 heart sound during a physical examination using a stethoscope. The S3 is low-pitched and often faint, best heard with the stethoscope’s bell, designed for low-frequency sounds. It is usually most audible over the heart’s apex, the left ventricle’s bottom-most tip.
To enhance detection, patients may lie in a left lateral decubitus position (on their left side), bringing the heart closer to the chest wall. Exhalation can also make the sound more discernible. If a pathological S3 is suspected, further diagnostic evaluations are usually performed. These include an echocardiogram to assess heart function, chamber size, and valve integrity.