The heart’s familiar “lub-dub” sound represents the first two heart sounds, known as S1 and S2, which occur as the heart valves close. A “heart gallop” refers to the presence of extra, low-frequency sounds that disrupt this rhythm, creating a three- or four-beat cadence often compared to a galloping horse. These abnormal sounds are designated S3 or S4, and their presence can signal significant underlying changes within the heart muscle or blood volume.
The Mechanics of the S3 and S4 Gallop
The third heart sound (S3), often called a ventricular gallop, occurs early in the heart’s resting phase (diastole). This sound occurs during the rapid filling of the ventricle shortly after the atrioventricular valve opens. The sound is thought to result from the sudden deceleration of blood as it hits a ventricle that is either poorly compliant or already overfilled with blood. An S3 sound indicates volume overload or a ventricle failing to contract effectively during the previous cycle.
The fourth heart sound (S4), referred to as an atrial gallop, occurs much later in diastole, just before the first heart sound (S1). This sound is caused by the atria contracting forcefully to push the remaining blood into a stiff or non-compliant ventricle. The stiffening of the ventricular wall resists this final push of blood, creating an audible vibration. The S4 sound is closely associated with conditions that cause the heart muscle to thicken or become rigid.
Assessing the Risk: Physiologic Versus Pathologic Sounds
The risk associated with a heart gallop depends on the patient’s age and context. An S3 sound can be considered “physiologic,” meaning normal and harmless, in specific populations, such as healthy children and young adults under the age of 40. This benign S3 is also common in trained athletes and pregnant women due to the higher-than-normal blood volume circulating through their hearts. The ventricles in these individuals are typically healthy and pliable, and the sound is a result of the rapid and excessive blood flow filling the chamber.
However, the presence of an S3 in an adult over the age of 40 is almost always a concerning sign, classifying it as a “pathologic” sound. In older adults, this sound strongly suggests a significant problem with the heart’s ability to pump or manage blood volume.
The S4 sound is rarely considered a normal or physiologic finding, even in younger individuals. Its presence usually indicates a decrease in the ventricle’s ability to relax and fill properly due to stiffness.
The S4 sound is a red flag because it reflects a stiff, less compliant ventricle, which is a structural abnormality. While a quiet S4 might be heard in some older adults, a loud or newly developed S4 is indicative of an underlying cardiac condition that requires immediate attention. The distinction between a harmless S3 and a pathologic S3 or S4 lies in the fundamental difference between a healthy, volume-overloaded heart and one that is structurally or functionally compromised.
Conditions Underlying a Pathologic Gallop
A pathologic S3 sound is an indicator of left ventricular systolic dysfunction, meaning the heart cannot effectively pump blood out of the main chamber. A primary cause in adults is congestive heart failure, where the heart is unable to handle the volume of blood returning to it, leading to volume overload. Other serious conditions that cause a pathologic S3 include severe valvular issues, such as mitral or tricuspid regurgitation. In these cases, blood flows backward, increasing the volume the ventricle must accommodate and generating the S3 sound upon filling.
The S4 sound is linked to conditions that cause the ventricle to become thick and rigid, impairing its ability to relax and fill during diastole. Uncontrolled high blood pressure is a primary cause, as the heart muscle thickens over time to pump against the high resistance, leading to left ventricular hypertrophy. Aortic stenosis, which is the narrowing of the aortic valve, also forces the ventricle to work harder and thicken, resulting in the S4 gallop. The presence of an S4 can also be a finding in patients experiencing acute myocardial ischemia, indicating active injury to the heart muscle.
Confirming the Diagnosis and Treatment Approach
When a heart gallop is detected, the physician typically orders tests to confirm the underlying cause rather than the sound itself. The primary diagnostic tool is an echocardiogram (Echo). This ultrasound of the heart provides detailed images of the heart’s structure, allowing physicians to assess the function of the valves, the thickness of the ventricular walls, and the overall pumping ability.
Blood tests, such as cardiac biomarkers like B-type natriuretic peptide (BNP), are also used to evaluate the presence and severity of heart failure. The gallop sound itself is not a disease that can be treated directly; management focuses entirely on resolving the underlying condition causing the abnormal sound. Treatment may involve medications like diuretics to reduce fluid overload, or ACE inhibitors and beta-blockers to manage blood pressure and improve the heart’s function. Successful treatment of the root disease improves the heart’s structural and functional abnormalities, which may cause the pathologic gallop sound to disappear.