It can mean several different things, as S4 is not diagnostic of any one particular problem, but simply a sign that several need to be ruled out. It can occur gradually, over time, with conditions such as pulmonary hypertension or hypertension related valve changes. It can onset rapidly due to cardiomyopathies such as a ventricular MI significantly decreasing ventricular compliance. In a younger adult, it usually means nothing, and can often be found by a particularly competent auscultator. But in middle age and older adults, it is always cause for concern and diagnostic follow-up. In the presence of hypertension, respiratory distress, or other signs of an MI, it is a red flag.
