The five abnormal heart sounds are murmurs, S3 gallops, S4 gallops, clicks, and rubs. Murmurs are turbulent flow through a valve or septal defect, S3 is early-diastolic filling into a volume-loaded ventricle, S4 is late-diastolic atrial push into a stiff ventricle, clicks are abrupt valve-opening sounds, and rubs are pericardial friction. Each maps to a distinct timing window in the cardiac cycle, which is why the stethoscope still beats most tests at the bedside.
The Cardiac Cycle as a Timing Map
Every abnormal sound earns its name from exactly where it lands between S1 and S2. S1 marks mitral and tricuspid closure at the start of systole. S2 marks aortic and pulmonary closure at end-systole. The gap between S2 and the next S1 is diastole, and it splits into early, mid, and late phases. A sound's position in that window is the single most useful diagnostic clue a clinician has.
Murmurs fill a segment of flow, so they run throughout systole or diastole rather than sitting at one instant. Gallops and clicks are discrete events, each occupying 20 to 60 milliseconds. Rubs are scratchy, triphasic noises tied to cardiac motion rather than blood flow. In plain terms: continuous noise means turbulent blood, and a single snap means a structure moving.
The physics is straightforward. Normal flow is laminar and silent below a Reynolds number of roughly 2,000. Turbulence appears when velocity rises or viscosity falls, producing audible vibration. Anemia drops viscosity, which is why a flow murmur can appear in a patient with normal valves but a hemoglobin of 7 g/dL.
Murmurs: The Turbulence Signal
A murmur is the most common of the 5 abnormal heart sounds and the one with the widest differential. Roughly 10 percent of adults have an audible murmur on careful auscultation, and only a minority reflect structural disease. The pathologic ones share three features: grade 3 or louder, a palpable thrill, and a harsh or blowing quality that radiates.
Grading runs I to VI. Grade I is barely audible in a quiet room. Grade III is easily heard and is the threshold where echocardiography becomes routine. Grade IV adds a thrill. Grade V is audible with the stethoscope edge lifted off the chest. Grade VI is audible without contact.
Systolic murmurs divide by timing relative to S1 and S2. Ejection murmurs are crescendo-decrescendo and stop before S2. Holosystolic murmurs run from S1 through S2, which points to mitral regurgitation, tricuspid regurgitation, or a ventricular septal defect. The 2020 ACC/AHA valvular heart disease guideline sets severe aortic stenosis at a peak velocity of 4.0 m/s or higher, a mean gradient of 40 mm Hg or more, and a valve area of 1.0 cm² or less.
Gallops: S3 and S4
The S3 gallop lands 120 to 200 milliseconds after S2, in early diastole, when blood decelerates against a ventricular wall. In a 20-year-old it can be normal. In a 60-year-old it carries a hazard ratio near 1.3 for heart failure hospitalization over five years. The dividing line is age and ventricular function, not the sound itself.
S4 arrives 40 to 100 milliseconds before S1, when the atrium contracts into a noncompliant ventricle. It is almost never normal in adults and is the classic sign of concentric hypertrophy, as seen in long-standing hypertension or aortic stenosis. A stiff ventricle needs atrial kick, which is why losing sinus rhythm in a patient with a loud S4 can precipitate decompensation.
Both gallops are low-frequency, so they demand the bell with light pressure. Pressing hard filters them out and creates a false negative. A single EKG lead plus the bell will outperform a rushed exam every time.
Clicks and Rubs: Structural Snapshots
Ejection clicks are high-frequency and occur 40 to 70 milliseconds after S1. Aortic valve clicks are best heard at the right second intercostal space. Pulmonary clicks sit at the left second space and move with inspiration, a detail that distinguishes them from aortic clicks. Mitral valve prolapse produces a mid-systolic click followed by a late systolic murmur.
Pericardial rubs are the outlier among the 5 abnormal heart sounds because they are not generated by blood. They arise from inflamed pericardial surfaces sliding against each other. They are triphasic in about half of cases, with components during ventricular contraction, ventricular filling, and atrial contraction. They may be transient, lasting minutes to hours, which explains why serial exams catch what a single one misses.
Timing Table: When Each Sound Occurs
| Sound | Cycle timing | Typical frequency | Best location | Common cause |
|---|---|---|---|---|
| Systolic murmur | S1 to S2 | 100-500 Hz | Depends on valve | Stenosis or regurgitation |
| S3 gallop | 120-200 ms after S2 | 20-80 Hz | Apex, bell | Volume overload |
| S4 gallop | 40-100 ms before S1 | 20-80 Hz | Apex, bell | Stiff ventricle |
| Ejection click | 40-70 ms after S1 | 200-800 Hz | Right or left 2nd space | Bicuspid aortic valve |
| Pericardial rub | All three phases | Mixed | Left sternal border | Pericarditis |
Comparison: Innocent Versus Pathologic Murmurs
| Feature | Innocent | Pathologic |
|---|---|---|
| Grade | I-II | III or higher |
| Timing | Early systolic, never holosystolic | Holosystolic or pan-diastolic |
| Radiation | None | Carotid, axilla, or back |
| Thrill | Absent | Often present |
| Palpitations or syncope | No | Possible |
| Echocardiogram yield | Low | High |
Timeline: From First Hearing to Diagnosis
| Time point | What happens | Action |
|---|---|---|
| 0-5 minutes | Auscultation identifies sound type | Document timing and grade |
| 5-15 minutes | Provocative maneuvers narrow cause | Squat, Valsalva, handgrip |
| Same visit | EKG identifies rhythm and hypertrophy | 12-lead EKG |
| 24-72 hours | Echocardiogram confirms structure | Order transthoracic echo |
| 1-2 weeks | Cardiology review if severe | Referral per 2020 ACC/AHA criteria |
| 1-3 months | Repeat exam if murmur unexplained | Serial auscultation |
Maneuvers That Separate the Five Sounds
Bedside maneuvers are the highest-yield tool a clinician can use, and they cost nothing. Squatting raises preload and afterload, which increases the murmur of mitral regurgitation and delays the click of mitral valve prolapse. Standing does the reverse and brings the click earlier. Valsalva strain reduces venous return and softens most murmurs except hypertrophic cardiomyopathy, which gets louder because the ventricle empties more completely.
Handgrip raises systemic vascular resistance and intensifies mitral regurgitation and ventricular septal defect murmurs while softening aortic stenosis. Inspiration increases right-sided flow, which is why tricuspid and pulmonary sounds swell and left-sided ones barely change.
A common misconception is that a loud murmur is more dangerous than a soft one. The counterintuitive detail: a soft, late-peaking murmur in severe aortic stenosis can signal worse disease than a loud early-peaking murmur, because the failing ventricle can no longer generate high velocity. Peak velocity falls below 3.0 m/s in low-flow states, and that is the patient who decompensates first.
Red Flags That Need Same-Day Evaluation
- A new murmur with fever and a positive blood culture
- Syncope, angina, or exertional dyspnea alongside a grade III murmur
- A diastolic murmur of any grade, which is never benign in adults
- A new S3 in a patient over 40 with jugular venous distension
- A rub with pleuritic chest pain and diffuse ST elevation
- Hypotension with a new holosystolic murmur, suggesting acute regurgitation
What to Actually Do
Start with the bell, in a quiet room, with the patient supine and then in the left lateral position. Listen at all four valve areas plus the left sternal border. Time the sound against the carotid upstroke, not against your memory of the cycle.
Grade every murmur and state whether it is systolic or diastolic. Diastolic murmurs earn an echocardiogram regardless of grade. Then apply provocative maneuvers to sharpen the differential before ordering tests.
Document the patient's position, phase of respiration, and the maneuver used. That record lets the next examiner reproduce your finding. When a murmur is new and the patient is stable, transthoracic echocardiography within a week resolves the question in more than 90 percent of cases.
Limits of Auscultation
Auscultation is operator-dependent, and agreement between examiners for faint sounds is modest. Studies of S3 detection show kappa values around 0.3 to 0.5 even among trained clinicians. Electronic stethoscopes improve high-frequency detection but have not consistently improved S3 accuracy.
Handheld ultrasound has changed the calculus. In trained hands, a pocket device can confirm valve pathology in under two minutes, and it is now used in emergency departments to triage murmurs. It does not replace formal echocardiography but shortens the time to the first correct answer.
The five abnormal heart sounds remain the fastest way to move from a patient's bedside to a working diagnosis. No machine has made them obsolete, because none matches the stethoscope's zero cost and instant feedback.