S3 Vs. S4 Heart Sounds: 7 Critical Differences That Reveal Your Heart's True Condition

The ability to distinguish between the Third Heart Sound (S3) and the Fourth Heart Sound (S4) is a cornerstone of cardiovascular diagnosis, yet it remains one of the most challenging skills in clinical medicine. As of December 2025, modern cardiology continues to emphasize the prognostic value of these extra sounds, often referred to as 'gallops,' as they provide immediate, non-invasive clues about the underlying mechanics of the heart—specifically, whether the problem is one of volume overload or ventricular stiffness. Understanding the subtle differences in their timing and acoustic properties is crucial for directing appropriate management, from treating acute heart failure to managing chronic hypertensive heart disease.

The presence of an abnormal heart sound, whether S3 or S4, signals a fundamental issue with the heart’s ability to fill properly during diastole. While both sounds are low-frequency, their occurrence in the cardiac cycle and the resulting clinical correlation—systolic dysfunction for S3 versus diastolic dysfunction for S4—dictate vastly different treatment pathways. This deep dive will clarify the seven most critical distinctions between these two vital acoustic biomarkers.

The Essential Biography of S3 and S4 Heart Sounds

The Third and Fourth Heart Sounds are considered 'extra' sounds, occurring in addition to the normal 'lub-dub' (S1 and S2). They are collectively known as gallop rhythms because, when heard together with S1 and S2, the cadence resembles a horse's gallop (e.g., "Ken-tuc-ky" for S3, or "Ten-nes-see" for S4).

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• S1 (First Heart Sound): Marks the start of systole (ventricular contraction), caused by the closure of the mitral and tricuspid valves.
• S2 (Second Heart Sound): Marks the end of systole and the start of diastole, caused by the closure of the aortic and pulmonic valves.
• S3 (Third Heart Sound): Occurs in early diastole, immediately following S2.
• S4 (Fourth Heart Sound): Occurs in late diastole, just before S1.

While an S3 can occasionally be a physiologic (normal) finding in children, young adults, and highly trained athletes, an S4 is almost always considered pathologic (abnormal) in all age groups, signifying a stiff or non-compliant ventricle.

1. Timing in the Cardiac Cycle: The Crucial Diastolic Difference

The most fundamental difference between S3 and S4 lies in their timing during the diastolic phase of the heart cycle.

• S3 Heart Sound: Early Diastole. The S3 occurs during the rapid ventricular filling phase, which is the first third of diastole. It is heard shortly after S2 (S2-S3). Think of it as the ventricle being overwhelmed by the sudden gush of blood.
• S4 Heart Sound: Late Diastole (Presystolic). The S4 occurs during the final phase of diastole, known as atrial contraction, just before S1 (S4-S1). It is a sound made by the atrium contracting and forcefully pushing blood into a stiff, resistant ventricle.

This timing difference is the key to auscultation. An S3 creates the rhythm S1-S2-S3, while an S4 creates the rhythm S4-S1-S2. A summation gallop occurs when both S3 and S4 are present, often at high heart rates, merging into a single, loud extra sound.

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2. The Underlying Pathophysiology: Volume vs. Pressure

The mechanism that generates each sound is entirely different and directly relates to the heart’s primary failure mode.

S3: The Volume Overload Sound

The S3 is generated by the sudden deceleration of blood as it rushes into a ventricle that is already filled with a large volume (volume overload) or a ventricle that has reduced contractility (systolic dysfunction). The ventricular walls suddenly hit their elastic limit, causing a vibration. Elevated left ventricular filling pressures are a hallmark of this condition.

S4: The Pressure Overload/Stiffness Sound

The S4 is generated when the atria contract forcefully to push the remaining blood volume into a stiff, non-compliant ventricle. This stiffness is typically due to chronic pressure overload, which causes the ventricular wall to thicken (hypertrophy). The force of the atrial kick against the stiff wall creates the audible S4 vibration.

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3. Clinical Correlation: Systolic vs. Diastolic Dysfunction

The most significant clinical takeaway is that S3 and S4 typically point to two different types of heart failure, which guides treatment.

• S3 Implication: Systolic Dysfunction. The presence of a pathological S3 in an adult is a strong indicator of Congestive Heart Failure (CHF), specifically heart failure with reduced ejection fraction (HFrEF). Conditions that cause a floppy, dilated heart, like dilated cardiomyopathy, are prime culprits.
• S4 Implication: Diastolic Dysfunction. The S4 is the classic sign of heart failure with preserved ejection fraction (HFpEF). It signifies a stiff ventricle unable to relax and fill properly. Conditions causing a thick, rigid heart, such as hypertensive heart disease, aortic stenosis, or myocardial ischemia, are highly associated with S4.

4. Auscultation Technique and Sound Quality

Both sounds are low-frequency, making them difficult to hear, but the specific technique for maximizing their audibility is identical.

• Low-Pitched Sound: Both S3 and S4 are best heard using the bell of the stethoscope, which is designed to pick up low-frequency sounds.
• Location: Both are usually best heard at the cardiac apex (mitral area) with the patient in the left lateral decubitus position.
• Maneuver: Both sounds are often accentuated (made louder) by maneuvers that increase venous return to the heart, such as raising the legs or having the patient exhale completely.

5. Specific Associated Cardiac Conditions

While the umbrella terms are systolic and diastolic dysfunction, specific diseases are strongly linked to each sound.

Conditions Associated with S3 Gallop:

• Mitral Regurgitation (MR)
• Severe Aortic Regurgitation
• Ventricular Septal Defect (VSD)
• High-output states (e.g., severe anemia, thyrotoxicosis)

Conditions Associated with S4 Gallop:

• Severe Hypertension (leading to Left Ventricular Hypertrophy)
• Acute Myocardial Infarction (MI)
• Hypertrophic Cardiomyopathy (HCM)
• Aortic Stenosis

6. Prognostic Significance: Which is Worse?

Both sounds are considered serious findings, but the S3 often carries a more immediately concerning prognosis.

The presence of a new S3 in an adult with symptoms of shortness of breath (dyspnea) is highly predictive of a poor outcome and is a strong independent predictor of mortality in patients with heart failure. New research has focused on using acoustic biomarkers like S3 amplitude, measured by advanced phonocardiography, to monitor the progression of New York Heart Association (NYHA) class in heart failure patients, confirming its role as a real-time indicator of worsening function.

7. Management Focus: Diuretics vs. Blood Pressure Control

The management strategy for a patient is fundamentally different based on which gallop sound is heard.

• S3 Management: The primary goal is to reduce the volume overload and improve contractility. Treatment focuses on diuretics (to reduce fluid) and medications to improve heart function, such as ACE inhibitors, beta-blockers, and ARNI therapy.
• S4 Management: The primary goal is to reduce the stiffness and pressure within the ventricle. Management focuses on aggressive blood pressure control (to reduce the afterload) and treating the underlying cause, such as managing coronary artery disease or controlling hypertension.

In summary, while both S3 and S4 are extra diastolic sounds, the S3 (early diastole) is a sign of a failing pump (systolic dysfunction/volume overload), and the S4 (late diastole) is a sign of a stiff chamber (diastolic dysfunction/pressure overload). Recognizing this critical distinction is the first step toward accurate diagnosis and life-saving treatment.

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Relevant Entities for Topical Authority

Diastole, Systole, Gallop Rhythm, Physiologic S3, Pathologic S4, Rapid Ventricular Filling, Atrial Contraction, Summation Gallop, Elevated Filling Pressures, Congestive Heart Failure (CHF), Dilated Cardiomyopathy, Hypertensive Heart Disease, Aortic Stenosis, Myocardial Ischemia, Mitral Regurgitation, Ventricular Septal Defect, Severe Hypertension, Acute Myocardial Infarction (MI), Hypertrophic Cardiomyopathy (HCM), Apex (of the heart), Venous Return, Phonocardiography, New York Heart Association (NYHA), Coronary Artery Disease, Early Diastole, Late Diastole, Echocardiography.