Additional heart sounds during early diastole in a patient with hypertrophic cardiomyopathy and atrioventricular block.

A third heart sound (S3) and a fourth heart sound (S4) are similarly perceived as low-pitched sounds and can be difficult to distinguish in some conditions, such as tachycardia or arrhythmia. We report a case with hypertrophic cardiomyopathy and Wenckebach second-degree atrioventricular block, in which the S4 was initially misdiagnosed as an S3 on auscultation and later confirmed using a phonocardiogram with an apexcardiogram. Interestingly, the amplitude of the S4 dynamically and regularly fluctuated in proportion to the interval between the S4 and the preceding ventricular contraction.