The five abnormal heart sounds are S3 (ventricular gallop), S4 (atrial gallop), murmurs, pericardial friction rubs, and clicks or snaps. In a healthy heart, you typically hear only two sounds: S1 (the “lub”) when the heart valves close as it begins pumping, and S2 (the “dub”) when valves close as it finishes pumping. Any additional sound beyond these two falls into one of the five categories above and can signal anything from a harmless variant to a serious heart condition.
S3: The Ventricular Gallop
The third heart sound, S3, is a low-pitched extra beat heard shortly after the normal S2. It happens during early diastole, the phase when the ventricles are rapidly filling with blood. The sound is produced when incoming blood suddenly decelerates as it hits the ventricular wall, causing the heart muscle and blood to vibrate together. Think of it like water rushing into a container and abruptly sloshing against the sides.
In adults over 30, an S3 almost always points to something abnormal. It’s closely linked to heart failure, where the ventricle is overstretched and holds too much blood. It also shows up with valve problems that allow blood to leak backward (regurgitation) and with holes between heart chambers that increase the volume of blood flowing into a ventricle. When present in a patient with heart failure, an S3 is one of the more reliable bedside indicators that the condition is worsening.
There’s an important exception: S3 can be completely normal in younger people. It’s readily heard in most children and young adults under 40. It’s also extremely common in pregnancy, reported in up to 80% of pregnant women, because of the natural increase in blood volume during that time.
S4: The Atrial Gallop
The fourth heart sound, S4, occurs just before S1, in the final moment of diastole when the atria contract to push the last bit of blood into the ventricles. You hear it when the atria have to squeeze against a ventricle that has become abnormally stiff. That stiffness forces the atria to work harder, and the extra effort produces a brief, low-pitched thump.
The most common cause of a stiff ventricle is chronic high blood pressure. Over time, the heart muscle thickens (hypertrophy) to compensate for pumping against elevated pressure, and thicker walls don’t relax as easily. An S4 is sometimes the earliest physical sign of hypertension’s effect on the heart. Other conditions that stiffen the ventricle include coronary artery disease, scarring (fibrosis) from a previous heart attack, and certain types of cardiomyopathy.
S4 sounds similar to S3, and the main way to tell them apart is timing. S4 comes right before the heartbeat (before S1), while S3 comes right after (after S2). When both are present, the combination creates a rapid three-beat rhythm called a “gallop” because it sounds like a horse running.
Murmurs: Turbulent Blood Flow
A heart murmur is a whooshing or swishing sound caused by turbulent blood flow through or near the heart. Normal blood flow is smooth and relatively quiet. When something disrupts that flow, whether a narrowed valve, a leaky valve, or an abnormal opening, the turbulence produces audible vibrations.
Murmurs are classified by when they occur in the heartbeat cycle:
- Systolic murmurs happen while the heart is pumping blood out. Common causes include a narrowed aortic valve (aortic stenosis) or a mitral valve that leaks backward (mitral regurgitation).
- Diastolic murmurs happen while the heart is filling with blood. A narrowed mitral valve or a leaky aortic valve can produce these.
- Continuous murmurs persist through the entire heartbeat and can indicate an abnormal connection between blood vessels.
Not all murmurs are dangerous. Benign (or “innocent”) murmurs are common in children and during pregnancy, where increased blood flow naturally creates some turbulence without any structural problem. In older adults, calcium buildup on the valve leaflets is a frequent culprit. The valves stiffen and narrow over time, or they stop closing completely, both of which create turbulence.
Clinicians grade murmur intensity on a scale from 1 to 6, with 1 being barely detectable and 6 being loud enough to hear without even placing a stethoscope on the chest. The grade helps track whether a murmur is getting worse over time, though loudness alone doesn’t always predict severity.
Pericardial Friction Rubs
A pericardial friction rub is a harsh, scratchy sound often compared to sandpaper being rubbed together. It comes from the pericardium, the thin two-layered sac surrounding the heart. Normally these layers glide silently against each other. When they become inflamed, a condition called pericarditis, the roughened surfaces create friction with every heartbeat.
The sound can have up to three components, corresponding to atrial contraction, ventricular contraction, and early ventricular filling. It’s typically loudest along the left edge of the breastbone, especially when a person sits up and leans forward. A pericardial rub is the hallmark physical finding of pericarditis. Diagnosing pericarditis requires at least two criteria: chest pain that worsens with breathing, this friction rub on exam, or characteristic changes on an electrocardiogram.
Rubs can come and go. A patient might have an audible rub during one exam that disappears hours later, which is why they’re sometimes missed. If fluid builds up between the pericardial layers (pericardial effusion), the rub may actually become quieter because the fluid acts as a cushion between the inflamed surfaces.
Clicks and Opening Snaps
Clicks and snaps are brief, high-pitched sounds produced by specific valve problems. Despite sounding similar to a non-expert ear, they come from different mechanisms and occur at different points in the heartbeat.
Ejection clicks happen in early systole, right after the heart begins pumping. They’re associated with valves that are structurally abnormal, typically from a congenital defect. In aortic or pulmonic stenosis, the abnormal valve creates sudden tension on the ventricular wall as it opens, producing a sharp click. A similar click can occur when high pressure in the lung arteries stretches the pulmonary valve open. Mid-to-late systolic clicks, on the other hand, are the signature sound of mitral valve prolapse, where a floppy valve leaflet billows backward and its supporting cords snap taut like a parachute catching wind.
Opening snaps occur in early diastole, just as the heart begins to fill. The classic cause is mitral stenosis, where a thickened mitral valve suddenly bulges downward under pressure. The snap happens at the moment the stiff leaflet reaches its limit and stops abruptly. In mitral stenosis, the timing of the snap relative to S2 provides a clue about severity: the shorter the gap, the higher the pressure buildup, and the more severe the narrowing.
How Abnormal Sounds Are Evaluated
A clinician listens for these sounds using a stethoscope at five standard points on the chest. The aortic area sits between the second and third ribs on the right side of the breastbone. The pulmonic area is in the same spot on the left. Erb’s point, between the third and fourth ribs on the left, picks up certain murmurs particularly well. The tricuspid area is between the fourth and fifth ribs, and the mitral area is at the bottom tip of the heart, roughly below the left nipple. Each location corresponds to a valve, so where a sound is loudest helps narrow down its source.
When an abnormal sound raises concern, the primary follow-up test is an echocardiogram, an ultrasound of the heart that shows valve movement, chamber size, and blood flow in real time. An electrocardiogram (ECG) measures the heart’s electrical activity and can reveal rhythm problems or signs of thickening. In cases where these tests aren’t conclusive, imaging such as a chest X-ray, CT scan, or MRI may be used. Cardiac catheterization, where a thin tube is threaded through a blood vessel to the heart, is reserved for situations where other tests haven’t pinpointed the cause.