Classification and Mechanisms of Cardiac Murmurs

Systolic Murmurs

• The American College of Cardiology states that systolic murmurs are generated by turbulent blood flow across normal or stenotic semilunar valves during ventricular ejection, typically crescendo-decrescendo in character 1
• Systolic murmurs increase in intensity after a ventricular premature beat or during long cycle lengths in atrial fibrillation due to increased stroke volume, as noted by the American College of Cardiology 2
• The American College of Cardiology recommends that early systolic murmurs, which begin with S1 and end in midsystole, be evaluated for tricuspid regurgitation without pulmonary hypertension or acute mitral regurgitation 1
• In large ventricular septal defects with pulmonary hypertension, the pressure equalization at end-systole eliminates the shunt, limiting the murmur to early systole, according to the American College of Cardiology 3
• Pansystolic murmurs are generated when blood flows between chambers maintaining widely different pressures throughout the entire systolic period, creating a plateau-shaped murmur from S1 to S2, as stated by the American College of Cardiology 4
• The American College of Cardiology identifies three primary causes of pansystolic murmurs: mitral regurgitation, tricuspid regurgitation, and ventricular septal defect, each with distinct clinical implications 4
• Late systolic murmurs start well after ejection begins and end before or at S2, typically soft to moderately loud and high-pitched at the left ventricular apex, often associated with mitral valve prolapse, as noted by the American College of Cardiology 5

Diastolic Murmurs

• The American College of Cardiology states that early diastolic murmurs begin with or shortly after S2 when ventricular pressure drops sufficiently below aortic or pulmonary artery pressure, and are often high-pitched and decrescendo, indicating aortic regurgitation or pulmonic regurgitation 2
• Middiastolic murmurs occur during early ventricular filling due to relative disproportion between valve orifice size and diastolic blood flow volume, usually originating from mitral and tricuspid valves, as noted by the American College of Cardiology 3
• The American College of Cardiology recommends that presystolic murmurs, which begin during ventricular filling that follows atrial contraction, be evaluated for mitral or tricuspid stenosis 5

Dynamic Auscultation for Differentiation

• The American College of Cardiology states that right-sided murmurs increase with inspiration due to increased venous return, while left-sided murmurs are louder during expiration 1
• Most murmurs decrease in length and intensity with the Valsalva maneuver, except for hypertrophic cardiomyopathy and mitral valve prolapse murmurs, which become louder, as noted by the American College of Cardiology 2
• The American College of Cardiology recommends that positional changes, such as standing and squatting, be used to evaluate murmurs, as most murmurs diminish with standing except hypertrophic cardiomyopathy and mitral valve prolapse 3

Clinical Significance and Diagnostic Approach

• The American College of Cardiology states that pansystolic murmurs almost always indicate pathological conditions requiring further evaluation, as they can lead to heart failure, pulmonary hypertension, and arrhythmias if untreated 4
• Echocardiography is the gold standard for confirming the cause of murmurs and should be performed in all patients with pansystolic murmurs of unknown cause, as recommended by the American College of Cardiology 6

Heart Murmur Auscultation Locations and Characteristics

Systolic Murmurs

• The American College of Cardiology recommends that aortic stenosis be listened for at the right upper sternal border (2nd right intercostal space), where it is best heard 7
• Aortic stenosis may radiate to the carotids bilaterally, as noted by the American College of Cardiology 7
• Mitral regurgitation is best heard at the cardiac apex (left ventricular apex), according to the American College of Cardiology 7
• Tricuspid regurgitation is best heard at the left lower sternal border, as recommended by the American College of Cardiology 7
• Ventricular septal defect is best heard at the left lower sternal border, where a pansystolic murmur can be detected, according to the American College of Cardiology 7
• Pulmonic stenosis is best heard at the left upper sternal border (2nd left intercostal space), with a midsystolic murmur, as noted by the American College of Cardiology 7

Diastolic Murmurs

• Aortic regurgitation is best heard at the left sternal border (3rd-4th intercostal space), with an early diastolic, high-pitched, decrescendo murmur, according to the American College of Cardiology 7
• Mitral stenosis is best heard at the cardiac apex, with a middiastolic or presystolic murmur, as recommended by the American College of Cardiology 7
• Tricuspid stenosis is best heard at the left lower sternal border, according to the American College of Cardiology 7
• Pulmonic regurgitation is best heard at the left upper sternal border, with a high-pitched, early diastolic murmur in patients with pulmonary hypertension, as noted by the American College of Cardiology 7
• Austin-Flint murmur (severe chronic AR) is best heard at the left ventricular apex, with a low-pitched, rumbling middiastolic or presystolic murmur, according to the American College of Cardiology 7

Key Clinical Pearls

• Right-sided murmurs increase with inspiration due to increased venous return, while left-sided murmurs are louder during expiration, as noted by the American College of Cardiology 7
• Standing causes most murmurs to diminish except HCM and MVP, which become louder, according to the American College of Cardiology 7
• Squatting increases most murmurs but softens HCM and MVP murmurs, as recommended by the American College of Cardiology 7

Auscultatory Findings and Diagnostic Evaluation of Mitral Stenosis

Murmur Characteristics

• The mitral stenosis murmur is a low‑pitched, rumbling, apical diastolic murmur best heard with the bell of the stethoscope and is characteristically preceded by an opening snap after the second heart sound. 8
• The murmur is middiastolic or presystolic, occurring during ventricular filling across the narrowed mitral orifice. 9
• It has a low‑pitched, rumbling quality that is optimally appreciated with light pressure of the bell on the skin. 9
• The murmur is loudest at the left ventricular apex and shows little radiation beyond the apex. 10

Opening Snap and Severity Correlation

• An opening snap follows the second heart sound (S2) and reflects the sudden tensing of stenotic mitral leaflets as they open in early diastole. 8
• The presence of an opening snap helps differentiate mitral stenosis from other causes of diastolic murmurs. 10
• The interval between S2 and the opening snap shortens as stenosis severity increases, mirroring rising left‑atrial pressure. 8

Dynamic Auscultation Maneuvers

• Exercise or any maneuver that raises heart rate shortens diastole, increases the transmitral gradient, and makes the murmur louder. 8

Associated Heart Sounds

• A loud first heart sound (S1) is common when mitral leaflets remain pliable, indicating forceful closure of the stenotic valve. 8
• With heavy calcification and advanced stenosis, S1 may become soft. 8
• Development of pulmonary hypertension in severe disease produces a loud second‑heart‑sound component (accentuated P2). 8

Clinical Presentation Pitfalls

• The murmur may be inaudible in patients with low cardiac output, obesity, chest‑wall deformities, or emphysema despite hemodynamically significant stenosis. 10
• Patients frequently present with nonspecific exertional dyspnea and an otherwise unrevealing physical examination, making the diagnosis easy to miss. 8

Diagnostic Confirmation with Echocardiography

• Transthoracic echocardiography (TTE) is mandatory for all patients with suspected mitral stenosis to confirm the diagnosis, quantify severity (mitral valve area, mean gradient, pulmonary artery pressure), and assess valve morphology. 8
• Physical‑examination findings alone are insufficient to grade severity; echocardiography provides the definitive hemodynamic assessment. 8