AuscultifyS4 Heart Sound (Atrial Gallop): Causes, Meaning and How to Hear It
The S4 heart sound is a low-pitched extra sound in late diastole, immediately before S1, produced when the atrium contracts into a stiff, non-compliant ventricle. It is almost always pathologic in adults and points to diastolic dysfunction from hypertension, left ventricular hypertrophy, aortic stenosis, hypertrophic cardiomyopathy or ischemia. Because it needs an atrial contraction, an S4 cannot occur in atrial fibrillation.
When does S4 occur?
S4 is the last sound of diastole. After passive filling slows, the atria contract and deliver the final 15 to 25 percent of ventricular filling, the atrial kick. In a normal ventricle that inflow is silent. In a stiff ventricle the atrial push raises pressure sharply and sets the ventricular wall vibrating, producing a dull sound a fraction of a second before the mitral and tricuspid valves close. The cadence is DUH-lub-dub, S4-S1-S2, the "TEN-nes-see" rhythm. S4 is therefore diastolic, not systolic, even though it sits right up against the start of systole.
S4 mechanism and why it is absent in AFib
S4 has two requirements: an effective atrial contraction and a ventricle with reduced compliance. Remove either and the sound disappears. That is why an S4 is impossible in atrial fibrillation, where the atria fibrillate rather than contract, and why it is also absent when the mitral valve is severely stenosed and the atrium cannot push blood through. If you think you hear a presystolic sound in an irregularly irregular rhythm, reconsider either the rhythm or the sound. See Can you hear S3 in AFib? for the full reasoning.
S4 causes
Anything that stiffens the ventricle can produce an S4. The common left ventricular causes are:
- Hypertensive heart disease and left ventricular hypertrophy, the most frequent cause in an outpatient population.
- Aortic stenosis, where an S4 in a younger patient suggests a significant gradient because it implies the LV has hypertrophied.
- Hypertrophic cardiomyopathy, where the S4 is often prominent and may be palpable.
- Acute myocardial ischemia or infarction. An S4 is so common during an acute MI that its absence is unusual; the ischemic myocardium stiffens within seconds.
- Diastolic dysfunction from any cause, including infiltrative disease early on, and heart failure with preserved ejection fraction.
A right ventricular S4 occurs with pulmonary hypertension and pulmonic stenosis. It is heard at the lower left sternal border, increases with inspiration, and may be accompanied by a prominent "a" wave in the jugular venous pulse.
Is S4 ever normal?
In adults an S4 should be treated as abnormal until proven otherwise. Some sources note a soft S4 in healthy older adults, attributed to the age-related decline in ventricular compliance, and it can occasionally be recorded in young people during vigorous exercise. Unlike S3, there is no age group in which an S4 is routinely expected. If you hear one, look for hypertension, LVH on the ECG, a murmur of aortic stenosis or a history of ischemia.
S4 vs S3 at a glance
| S4 (atrial gallop) | S3 (ventricular gallop) | |
|---|---|---|
| Timing | Late diastole, just before S1 | Early diastole, just after S2 |
| Cadence | DUH-lub-dub, "TEN-nes-see" | lub-dub-DUH, "Ken-TUCK-y" |
| Mechanism | Atrial contraction into a stiff ventricle | Rapid filling into a volume-loaded or dilated ventricle |
| Needs atrial contraction? | Yes, absent in AFib | No, persists in AFib |
| Ventricle | Thick, stiff, often normal size | Dilated, floppy |
| Typical causes | Hypertension, LVH, AS, HCM, ischemia | Systolic heart failure, MR, AR, high output |
| Normal variant? | Rarely, and only in older adults per some sources | Yes, in children, young adults, athletes, pregnancy |
The full comparison lives on the hub page S3 vs S4 heart sounds, and the mnemonic is unpacked in S3 Kentucky, S4 Tennessee.
Where is S4 best heard and what does it sound like?
A left ventricular S4 is loudest at the apex with the bell applied lightly, patient in the left lateral decubitus position, at end-expiration. It sounds like a soft, dull thud that seems to lean into S1, as if S1 had a short low-pitched run-up. It is often easier to feel than to hear: rest your fingertips over the apex and you may sense a double impulse, a presystolic bump followed by the main apical thrust. Firm pressure with the bell makes a true S4 fade, which is a useful bedside test.
S4 or split S1?
This is the commonest confusion. Both give a doubled sound around S1, but they differ in every other respect:
- Pitch: S4 is low and dull; the two components of a split S1 are both high and crisp.
- Chest piece: S4 is heard with the bell and disappears with firm pressure; a split S1 is best heard with the diaphragm and does not change with pressure.
- Site: S4 is loudest at the apex; a split S1 is loudest at the lower left sternal border, where the tricuspid component is heard.
- Rhythm: S4 is impossible in atrial fibrillation; a split S1 is not.
An ejection click also follows S1 closely, but it is high-pitched and falls after S1, whereas S4 falls before it.
Summation gallop
When both an S3 and an S4 are present and the heart rate rises above roughly 100 beats per minute, diastole shortens until the two sounds merge into a single loud mid-diastolic summation gallop, which can be louder than S1 or S2. Slowing the rate, for example with carotid sinus massage in an appropriate patient, separates the two sounds again into a four-beat quadruple rhythm.
How to document an S4
Record the site, position, chest piece and respiratory behaviour: "Low-pitched presystolic S4 at the apex with the bell in left lateral decubitus, absent at LLSB, no respiratory variation." Note the rhythm, since an S4 in a regular rhythm supports the finding and an S4 in an irregular rhythm should prompt a second listen. Add the blood pressure, apex character and any systolic murmur so the reader can connect the sound to a cause.
Learn S4 from real recordings in Auscultify
Auscultify's library includes real S4 recordings at the apex, alongside S3, split S1 and ejection clicks so you can hear the differences that this page describes. The Heart Sounds quiz mode drills them unlabelled, spaced repetition brings back the ones you miss, and the Spectrogram view (Pro) shows the low-frequency S4 sitting just ahead of S1.
Train heart sounds free →FAQ
What is an S4 heart sound?
S4 is a low-pitched extra heart sound in late diastole, immediately before S1, produced when the atrium contracts and pushes blood into a stiff, non-compliant ventricle. It is also called the atrial gallop or presystolic gallop.
When does S4 occur?
S4 occurs at the very end of diastole, during atrial contraction, just before the mitral and tricuspid valves close to produce S1. The cadence is DUH-lub-dub, the Tennessee rhythm.
Is S4 systolic or diastolic?
S4 is diastolic. It is the last event of diastole, coinciding with atrial systole, and it precedes the S1 that starts ventricular systole.
What does S4 indicate?
An S4 indicates a stiff, poorly compliant ventricle, in other words diastolic dysfunction. Common causes are hypertensive heart disease, left ventricular hypertrophy, aortic stenosis, hypertrophic cardiomyopathy and acute myocardial ischemia or infarction.
Where is S4 best heard?
A left ventricular S4 is best heard with the bell at the apex with the patient in the left lateral decubitus position. A right ventricular S4 is heard at the lower left sternal border and gets louder with inspiration.
Is S3 or S4 associated with heart failure?
Both can be. S3 is the classic sign of systolic heart failure with a dilated, volume-loaded ventricle. S4 is associated with diastolic dysfunction and heart failure with preserved ejection fraction, where the ventricle is stiff rather than dilated.