The heart produces sounds as it pumps blood throughout the body. Listening to these sounds is a foundational part of a medical examination. While some heart sounds are normal, others can signal underlying health conditions. Understanding these sounds provides insights into cardiac function.
The Heart’s Basic Sounds
The heart’s “lub-dub” rhythm consists of two primary sounds, S1 and S2. S1, the “lub,” occurs when the mitral and tricuspid valves close at the beginning of systole, the heart’s contraction phase. This prevents blood from flowing backward into the atria as ventricles pump blood out. S2, the “dub,” is generated by the closure of the aortic and pulmonic valves at the end of systole, marking the beginning of diastole, the heart’s relaxation and filling phase. These sounds result from heart valves snapping shut, creating vibrations as blood flow halts.
The Third Heart Sound
Beyond the “lub-dub,” a third heart sound, S3, can sometimes be heard. S3 is a low-frequency, brief sound that occurs early in diastole, shortly after S2. It is often described as a “ventricular gallop” because, when combined with S1 and S2, it can create a rhythm resembling a galloping horse. This sound arises from the rapid filling of the ventricles when blood rushes in from the atria.
S3 can be categorized as either physiological or pathological. A physiological S3 is normal, commonly heard in children, young adults, well-trained athletes due to compliant ventricles and increased blood volume, and in late pregnancy. It does not indicate a heart problem and usually disappears by middle age. Conversely, a pathological S3 in adults, especially over 40, often signals an underlying heart condition.
Distinguishing S3 from a Murmur
S3 heart sounds and heart murmurs are distinct phenomena with different origins and characteristics. A heart murmur is a prolonged sound, often described as a “whoosh” or “swish,” caused by turbulent blood flow. This turbulence results from narrowed, leaky, or malformed heart valves, or other structural issues within the heart or blood vessels. Murmurs can occur during systole (when the heart contracts), diastole (when it relaxes and fills), or continuously throughout the cardiac cycle.
In contrast, an S3 is a discrete, brief, low-pitched sound, not a continuous whooshing noise. It relates to the rapid filling of the ventricle during early diastole, rather than turbulent flow through a valve. Murmurs are caused by structural problems affecting blood flow dynamics, whereas S3 relates to the ventricle’s ability to accommodate incoming blood, reflecting its compliance or the volume of blood it receives. The timing, duration, and underlying mechanisms clearly differentiate an S3 from a heart murmur.
When S3 Requires Attention
While a physiological S3 is harmless, a pathological S3 in an adult warrants medical evaluation. A pathological S3 is associated with conditions leading to increased ventricular filling pressures or volume overload. It indicates heart failure, particularly when the heart’s pumping function is impaired. In heart failure, a weakened or stiff ventricle may struggle to effectively pump blood, leading to rapid and excessive filling that generates the S3 sound.
Other conditions causing a pathological S3 include severe anemia, thyroid overactivity, kidney failure, or significant valve regurgitation where blood leaks backward into the heart chambers. A newly developed or persistent S3 in an adult can be an early sign of ventricular dysfunction, indicating the need for further diagnostic tests like an echocardiogram to assess heart structure and function. Its presence can provide important information for diagnosis and treatment planning for cardiac ailments.