Heart sounds are the acoustic manifestations of cardiac mechanical activity. Understanding their origin and characteristics is essential for cardiac auscultation and diagnosis of valvular and structural heart disease.
Normal Heart Sounds
First Heart Sound (S1)
Timing: Beginning of systole (after QRS complex)
Mechanism: Closure of the mitral and tricuspid valves
Components:
- M1: Mitral valve closure (loudest at apex)
- T1: Tricuspid valve closure (loudest at left lower sternal border)
Interval M1-T1: Normally 20-30 ms (tricuspid closes after mitral)
Characteristics:
- Lower pitched than S2
- Best heard at the apex (mitral) and left lower sternal border (tricuspid)
- Coincides with the carotid upstroke (carotid pulse)
| S1 Intensity | Cause |
|---|---|
| Loud | Short PR interval, mitral stenosis, hyperdynamic state |
| Soft | Long PR interval, heart failure, mitral regurgitation, obesity |
| Variable | Atrial fibrillation, complete heart block |
Second Heart Sound (S2)
Timing: End of systole (after T wave)
Mechanism: Closure of the aortic and pulmonary valves
Components:
- A2: Aortic valve closure (loudest at right upper sternal border)
- P2: Pulmonary valve closure (loudest at left upper sternal border)
Physiologic splitting:
- Inspiration: A2-P2 interval widens (40-60 ms)
- Expiration: A2-P2 interval narrows (10-30 ms)
Mechanism of splitting:
- Inspiration increases venous return to the right heart
- Right ventricular ejection is prolonged
- Pulmonary valve closure is delayed
| S2 Splitting | Pattern | Cause |
|---|---|---|
| Physiologic | Widens on inspiration, narrows on expiration | Normal |
| Wide, fixed | Splitting constant with respiration | Atrial septal defect |
| Wide, variable | Wide splitting, varies with respiration | RBBB, pulmonary stenosis |
| Paradoxical (reverse) | Splitting narrows on inspiration, widens on expiration | LBBB, aortic stenosis |
| Single | No audible splitting | Tetralogy of Fallot, pulmonary atresia |
S2 intensity:
- Loud A2: Systemic hypertension
- Loud P2: Pulmonary hypertension
- Soft S2: Aortic stenosis (calcified valve)
S3 Gallop
Timing: Early diastole (after S2, during rapid ventricular filling)
Mechanism: Rapid ventricular filling abruptly limited by the ventricular wall
Characteristics:
- Low-pitched, dull sound
- Best heard at the apex with the bell
- Normal in children and young adults (< 40 years)
- Pathologic in older adults
Left-sided S3:
- Best heard at apex, left lateral decubitus position
- Indicates: LV dysfunction, volume overload, heart failure
- Associated with: Dilated cardiomyopathy, mitral regurgitation
- Ventricular gallop
Right-sided S3:
- Best heard at left lower sternal border
- Indicates: RV dysfunction, pulmonary hypertension
- Associated with: Cor pulmonale, pulmonary embolism
S4 Gallop
Timing: Late diastole (just before S1)
Mechanism: Atrial contraction against a stiff, noncompliant ventricle
Characteristics:
- Low-pitched, soft sound
- Best heard at the apex with the bell
- Always pathologic (indicates diastolic dysfunction)
Left-sided S4:
- LV hypertrophy (hypertension, aortic stenosis)
- Hypertrophic cardiomyopathy
- Acute myocardial infarction
- Atrial gallop
Right-sided S4:
- RV hypertrophy (pulmonary hypertension, pulmonary stenosis)
- Best heard at left lower sternal border
Extra Heart Sounds
Ejection Click
Timing: Early systole (after S1)
Mechanism: Opening of a stenotic semilunar valve or the sudden halt of a dilated great vessel
| Click | Location | Cause |
|---|---|---|
| Aortic | Apex (radiates) | Bicuspid aortic valve, aortic stenosis |
| Pulmonary | Left upper sternal border | Pulmonary stenosis, pulmonary hypertension |
Mid-Systolic Click
Timing: Mid-to-late systole
Mechanism: Prolapse of the mitral valve (or tricuspid)
Associated murmur: Late systolic murmur (if regurgitation occurs)
Cause: Mitral valve prolapse (MVP), myxomatous degeneration
Maneuvers:
- Squatting: Click moves later (increased preload)
- Standing: Click moves earlier (decreased preload)
Opening Snap
Timing: Early diastole (after S2)
Mechanism: Opening of a stenotic mitral valve
Characteristics:
- High-pitched, snapping sound
- Best heard at the apex
- Present in mitral stenosis (pliable valve)
Time interval: A2-OS:
- Short interval (< 70 ms): Severe mitral stenosis
- Long interval (> 100 ms): Mild mitral stenosis
Pericardial Knock
Timing: Early diastole
Mechanism: Sudden halt of ventricular filling due to pericardial constriction
Characteristics:
- Medium-pitched
- Best heard at the apex
- Associated with: Constrictive pericarditis
Heart Murmurs
Classification
| Characteristic | Types |
|---|---|
| Timing | Systolic, diastolic, continuous |
| Shape | Crescendo, decrescendo, plateau, crescendo-decrescendo |
| Location | Aortic, pulmonary, tricuspid, mitral |
| Intensity | Grade 1-6 |
| Pitch | High, medium, low |
| Quality | Blowing, harsh, rumbling, musical |
| Radiation | Carotid, axilla, back |
Murmur Grading
| Grade | Description |
|---|---|
| 1/6 | Very faint, heard only with effort |
| 2/6 | Faint, heard immediately |
| 3/6 | Moderate intensity, no thrill |
| 4/6 | Loud, palpable thrill |
| 5/6 | Very loud, heard with stethoscope edge on chest |
| 6/6 | Heard with stethoscope off the chest |
Systolic Murmurs
Holosystolic (pansystolic):
| Diagnosis | Location | Radiation | Characteristics |
|---|---|---|---|
| Mitral regurgitation | Apex | Axilla | Blowing, high-pitched |
| Tricuspid regurgitation | LLSB | Right | Increases with inspiration |
| VSD | LLSB | Diffuse | Harsh |
Mid-systolic (ejection):
| Diagnosis | Location | Radiation | Characteristics |
|---|---|---|---|
| Aortic stenosis | RUSB | Carotids | Harsh, crescendo-decrescendo |
| Pulmonary stenosis | LUSB | Left lung | Harsh, with ejection click |
| HOCM | LLSB-apex | Variable | Increases with Valsalva |
Late systolic:
- Mitral valve prolapse (with click)
- Papillary muscle dysfunction
Diastolic Murmurs
Early diastolic (decrescendo):
| Diagnosis | Location | Characteristics |
|---|---|---|
| Aortic regurgitation | LLSB | Blowing, high-pitched, decrescendo |
| Pulmonary regurgitation | LUSB | Similar, with pulmonary HTN |
Mid-to-late diastolic:
| Diagnosis | Location | Characteristics |
|---|---|---|
| Mitral stenosis | Apex | Low-pitched, rumbling, presystolic accentuation |
| Tricuspid stenosis | LLSB | Rumbling, increases with inspiration |
Continuous Murmurs
- Patent ductus arteriosus (left infraclavicular, machinery murmur)
- Arteriovenous fistula
- Venous hum (cervical, disappears lying down)
Maneuvers Affecting Heart Sounds and Murmurs
| Maneuver | Physiologic Effect | Auscultatory Change |
|---|---|---|
| Inspiration | ↑ RV preload, ↓ LV preload | ↑ Right-sided sounds, ↓ Left-sided |
| Expiration | ↓ RV preload, ↑ LV preload | ↓ Right-sided sounds, ↑ Left-sided |
| Valsalva (strain) | ↓ Preload (both sides) | MV click moves earlier, HOCM louder, AS softer |
| Squatting | ↑ Preload, ↑ Afterload | MV click later, HOCM softer, MR louder |
| Standing | ↓ Preload, ↓ Afterload | MV click earlier, HOCM louder |
| Handgrip | ↑ Afterload | MR louder, AR louder, AS softer |
| Amyl nitrite | ↓ Afterload | AS louder, MR softer, VSD louder |
Innocent Murmurs
| Type | Age | Location | Characteristics |
|---|---|---|---|
| Still murmur | 3-6 years | LLSB-apex | Vibratory, musical |
| Pulmonary flow murmur | Children | LUSB | Soft, systolic, ejection |
| Venous hum | Children | Infraclavicular | Continuous, disappears lying down |
| Supraclavicular bruit | Adolescents | Supraclavicular | Systolic, from great vessels |
| Mammary souffle | Pregnancy | Anterior chest | Continuous, from breast vessels |
Age-Related Changes
| Age | Normal Findings |
|---|---|
| Newborn | S2 single (pulmonary resistance high), murmurs from PDA |
| Children | Physiologic S3, innocent murmurs common |
| Young adults | Physiologic splitting of S2 |
| Middle-aged | S4 may appear (LV stiffness) |
| Elderly | Aortic sclerosis murmur, S4, reduced S2 intensity |