ACCS Respiratory Practice Exam 2026 – The Comprehensive All-in-One Guide to Exam Success!

S4 is an extra heart sound produced by the atrium contracting against a stiff, noncompliant ventricle. This late diastolic sound indicates conditions that make the ventricle less stretchy, so the atrial kick has to push into a rigid cavity. Because of that reduced compliance, S4 points to an underlying cardiac abnormality rather than a normal heart.

In practice, S4 is commonly associated with structural or functional changes like prior myocardial infarction or cardiomegaly (often with left ventricular hypertrophy), where the ventricle has become stiff. Dehydration, which reduces filling, does not create this stiff-ventricle situation, so S4 is not expected there. While valvular stenosis can lead to changes in the heart that might produce an S4, it is not the sole or defining cause, and S4 more broadly reflects a noncompliant ventricle due to various cardiac pathologies.