What heart sound is often noted in hypertrophic cardiomyopathy?

In hypertrophic cardiomyopathy (HCM), the presence of an S4 heart sound is commonly noted. The S4 sound, also known as the "atrial gallop," results from the vigorous contraction of the atria against a stiff and hypertrophied left ventricular wall. This occurs due to the impaired diastolic filling of the ventricle, which is characteristic of HCM.

HCM leads to increased ventricular stiffness and decreased compliance, causing the left ventricle to struggle to accommodate blood during atrial contraction. Therefore, the forceful atrial contraction generates the S4 sound just prior to the S1 sound when the heart is contracting.

While an S3 sound can indicate heart failure or volume overload, it is not as closely associated with hypertrophic cardiomyopathy. Heart murmurs, particularly those due to left ventricular outflow obstruction, are indeed common in HCM but do not specifically denote the characteristic heart sound referred to in the question. A split S2 is more closely associated with conditions like pulmonic stenosis or right bundle branch block and doesn't provide the same diagnostic indication in the context of HCM.