Normal Equine S3 Sounds

Amara Estrada, DVM, DACVIM (Cardiology) University of Florida

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The S1, S2, and S3 sounds can be heard in this recording; these are normal findings when auscultating a horse. 

A normal first heart sound (associated with closure and tensing of the mitral and tricuspid valves) can be appreciated at the onset of systole coinciding with the QRS complex on ECGs.  The S1 sound is longer, louder, and lower pitched than the second heart sound; the second heart sound is associated with closure of the aortic and pulmonic valves at the end of systole, following the T wave on the ECG. The third and fourth heart sounds occur during diastole and can often be auscultated in normal horses. Early, rapid ventricular filling generates the S3 sound, whereas the S4 sound is heard just before the S1 sound and occurs just after the P wave on the ECG. 

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