Heart sounds are produced by the mechanical events of the cardiac cycle—primarily the closure of heart valves. These sounds can be heard during auscultation and provide valuable information about cardiac function.
Normal heart sounds include S1 (first heart sound) and S2 (second heart sound) . Additional sounds, such as S3 and S4 , and murmurs , may indicate physiological or pathological changes.
Normal Heart Sounds
First Heart Sound (S1)
- Cause : Closure of the atrioventricular (AV) valves—mitral (M1) and tricuspid (T1).
- Timing : Marks the beginning of systole .
- Auscultation : Heard best at the apex of the heart.
- Physiological Note : M1 slightly precedes T1, though typically perceived as a single sound.
- Clinical Correlates :
- Increased : Mitral stenosis (due to elevated left atrial pressure).
- Decreased : Low cardiac output states.
Second Heart Sound (S2)
- Cause : Closure of the semilunar valves—aortic (A2) and pulmonary (P2).
- Timing : Marks the end of systole .
- Auscultation : Loudest at the base (left sternal border, 2nd intercostal space).
- Characteristics :
- Shorter, softer , and higher-pitched than S1.
- Clinical Correlates :
- Increased A2 : Systemic hypertension.
- Increased P2 : Pulmonary hypertension.
- Decreased : Aortic stenosis, aortic regurgitation, low output states.
Splitting of S2
- Normal (Physiological) :
- During inspiration , venous return to the right heart increases → delays P2.
- Blood is pooled in lungs → reduced return to left heart → A2 occurs earlier.
- Heard best at 2nd left intercostal space .
- Abnormal Splitting :
- Wide splitting : Pulmonary stenosis, right bundle branch block (RBBB), mitral regurgitation, VSD.
- Fixed splitting : Atrial septal defect (ASD).
- Paradoxical (reverse) splitting : Aortic stenosis, left bundle branch block (LBBB), hypertrophic cardiomyopathy (HOCM).
Mnemonic :
🫁 “moRe to the Right, Less to the Left” — during inspiration, right heart volume increases; left heart volume decreases.
Extra Heart Sounds
Third Heart Sound (S3) – “Ventricular Gallop”
- Timing : Early diastole, just after S2.
- Cause : Rapid ventricular filling; vibrations of the ventricular walls.
- Normal in:
- Children
- Young adults
- Athletes
- Pathologic (S3) : Associated with systolic heart failure , dilated cardiomyopathy.
- Sound : Low-pitched, best heard with the bell at the apex in left lateral decubitus position.
- Rhythm : Gallop
Fourth Heart Sound (S4) – “Atrial Gallop”
- Timing : Late diastole (presystole), just before S1.
- Cause : Atrial contraction against a non-compliant ventricle .
- Always pathologic .
- Conditions :
- Hypertension
- Aortic stenosis
- Ischemic heart disease
- Left ventricular hypertrophy
- Sound : Low-pitched; best heard at the apex with the bell.
Summation Gallop
- When S3 and S4 coexist , particularly in tachycardia , they may merge to form a summation gallop , indicating severe ventricular dysfunction.
Opening Snap (OS)
- Timing : Early diastole.
- Cause : Opening of a stenotic mitral valve.
- Best heard : At the apex or left lower sternal border .
- Often seen in mitral stenosis .
Heart Murmurs
Definition
A murmur is a blowing, swooshing sound caused by turbulent blood flow , usually across a heart valve.
Classification
1. Physiologic (Innocent) Murmurs
- Due to increased blood flow through normal valves.
- Conditions: Fever, pregnancy, anemia, exercise, thyrotoxicosis.
- Features:
- Always systolic .
- Soft, short , early peaking.
- Best heard at the base of the heart.
- Normal physical exam otherwise.
2. Pathologic Murmurs
- Due to valvular abnormalities (stenosis or regurgitation).
- May be systolic or diastolic .
Systolic Murmurs
Occur between S1 and S2
a. Midsystolic Ejection Murmur
- Shape : Crescendo-decrescendo.
- Location : Aortic or pulmonary area.
- Causes :
- Aortic stenosis
- Pulmonary stenosis
- Can be physiological
b. Late Systolic Murmur
- Begins after a gap following S1.
- Often associated with mitral valve prolapse or mitral regurgitation .
c. Pansystolic (Holosystolic) Murmur
- Extends from S1 to S2 without variation in pitch or intensity.
- Causes :
- Mitral regurgitation
- Tricuspid regurgitation
- Ventricular septal defect (VSD)
Diastolic Murmurs
Occur after S2 and are always pathological
a. Early Diastolic Murmur
- Starts with S2.
- High-pitched , decrescendo quality.
- Causes :
- Aortic regurgitation
- Pulmonary regurgitation
b. Mid-Diastolic Murmur
- Occurs in mid-to-late diastole.
- Low-pitched , rumbling sound.
- Best heard at the apex (mitral) or left lower sternal border (tricuspid).
- Causes :
- Mitral stenosis
- Tricuspid stenosis
Summary Table: Heart Sounds and Murmurs
| Sound/Murmur | Timing | Cause | Clinical Correlate |
|---|---|---|---|
| S1 | Beginning systole | AV valve closure | Loud in MS, soft in low output |
| S2 | End of systole | Semilunar valve closure | Split during inspiration |
| S3 | Early diastole | Rapid ventricular filling | HF, volume overload |
| S4 | Late diastole | Atrial contraction into stiff ventricle | LVH, ischemia, AS |
| Midsystolic murmur | Mid-systole | Flow across semilunar valve | AS, PS |
| Pansystolic murmur | Throughout systole | Regurgitation or VSD | MR, TR, VSD |
| Diastolic murmur | After S2 | Semilunar or AV valve pathology | AR, MS |
