Types of Heart Sounds Explained: Normal and Abnormal Heart Sounds (S1–S4)

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Types of Heart Sounds – Complete Guide

Introduction

Heart sounds are produced by the opening and closing of heart valves during the cardiac cycle. They are best heard using a stethoscope and provide important clues about heart function and disease. Normally, two heart sounds are heard, but additional sounds may indicate abnormalities.

1. Normal Heart Sounds

🔹 First Heart Sound (S1) – “Lub”

  • Caused by closure of mitral and tricuspid valves

  • Occurs at the start of systole

  • Loudest at the apex of the heart

  • Indicates beginning of ventricular contraction

🔹 Second Heart Sound (S2) – “Dub”

  • Caused by closure of aortic and pulmonary valves

  • Occurs at the end of systole

  • Best heard at the base of the heart

  • Marks the beginning of diastole

🫀 Normal rhythm: Lub–Dub

2. Systolic Murmur

A systolic murmur occurs between S1 and S2.

Causes:

  • Aortic stenosis

  • Mitral regurgitation

  • Ventricular septal defect (VSD)

  • Increased blood flow (anemia, pregnancy)

Characteristics:

  • Heard during ventricular contraction

  • Described as blowing or whooshing sound

  • May be innocent or pathological

3. Diastolic Murmur

Occurs after S2 during ventricular relaxation.

Causes:

  • Mitral stenosis

  • Aortic regurgitation

  • Pulmonary valve disorders

Features:

  • Always considered abnormal

  • Low-pitched, rumbling sound

  • Indicates serious heart disease

4. Third Heart Sound (S3) – Ventricular Gallop

  • Occurs just after S2

  • Sounds like: Lub–Dub–Dub

  • Caused by rapid filling of ventricle

Seen in:

  • Heart failure

  • Dilated cardiomyopathy

  • Normal in children and athletes

5. Fourth Heart Sound (S4) – Atrial Gallop

  • Occurs just before S1

  • Due to forceful atrial contraction

  • Indicates stiff ventricle

Seen in:

  • Hypertension

  • Myocardial infarction

  • Left ventricular hypertrophy

⚠️ Absent in atrial fibrillation

6. Gallop Rhythm

When S3 or S4 is present with normal heart sounds, it creates a galloping rhythm.

🔹 S3 Gallop – Heart failure
🔹 S4 Gallop – Hypertension or ischemic heart disease

Summary Table

Heart SoundTimingCauseSignificance
S1Start of systoleAV valve closureNormal
S2End of systoleSemilunar valve closureNormal
S3Early diastoleRapid fillingHF / Normal in youth
S4Late diastoleAtrial contractionPathological
MurmurAny phaseTurbulent blood flowAbnormal

Conclusion

Heart sounds are an essential part of cardiovascular examination. Understanding their timing, cause, and clinical significance helps in early diagnosis of heart diseases. Proper auscultation skills are crucial for nurses, doctors, and healthcare professionals.


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