Third Heart Sound

Definition

The third heart sound, commonly referred to as S3, is a low-frequency sound that occurs shortly after the second heart sound (S2) during the rapid filling phase of the ventricles in the cardiac cycle. This sound is typically associated with the early diastole when blood flows into the ventricles from the atria, and its presence can indicate various physiological or pathological conditions depending on the context.

5 Must Know Facts For Your Next Test

1. S3 is often described as a 'gallop' rhythm when it is present, creating a sound similar to 'lub-dub-ta' where 'ta' represents the third sound.
2. While S3 can be normal in young people and athletes, it may indicate heart failure or volume overload in older adults.
3. The mechanism behind S3 is primarily related to the sudden deceleration of blood flow into the ventricles during early diastole.
4. Third heart sound can be best heard with a stethoscope at the apex of the heart when the patient is in a left lateral decubitus position.
5. In clinical practice, identifying S3 can help in assessing ventricular function and determining potential heart complications.

Review Questions

• What is the significance of the third heart sound in relation to heart function and conditions?
  • The third heart sound (S3) is significant as it reflects how well the ventricles are filling with blood during diastole. Its presence can be a normal finding in younger individuals but may indicate underlying health issues such as heart failure or volume overload in older patients. Understanding this distinction helps healthcare providers evaluate cardiac function and decide on further diagnostic steps.
• How does the timing of the third heart sound relate to other components of the cardiac cycle?
  • The third heart sound occurs after the second heart sound (S2) during early diastole, specifically during the rapid filling phase when blood rushes into the ventricles from the atria. It follows S2, which marks the end of ventricular systole. Recognizing this timing helps clinicians differentiate between normal and abnormal findings based on when sounds are detected in relation to each other.
• Evaluate how factors such as age and physical condition can influence the presence of the third heart sound.
  • The presence of a third heart sound can vary significantly depending on age and physical condition. In younger individuals or athletes, S3 may be a normal finding due to increased blood flow and compliance of their ventricular walls. Conversely, in older adults or those with certain cardiovascular diseases, S3 may suggest pathological conditions such as congestive heart failure or volume overload. Understanding these influences aids in clinical assessment and highlights the importance of patient history in interpreting heart sounds.

Related terms

Cardiac Cycle: The sequence of events that occur during one heartbeat, encompassing both systole (contraction) and diastole (relaxation) phases.

Heart Sounds: The sounds produced by the heart during its activity, primarily including the first heart sound (S1), second heart sound (S2), and third heart sound (S3).

Diastole: The phase of the cardiac cycle where the heart muscle relaxes and allows the chambers to fill with blood.