A rapid heart rate and a gallop sound are auscultated in this sound.
The third and fourth heart sounds occur during diastole and are not audible in normal cats; S3 and S4 heart sounds are lower frequency than S1 and S2 and are usually best appreciated with the stethoscope bell. When heard, S3 or S4 sounds may be similar to horse galloping, hence the term gallop heart sounds; however, the term gallop rhythm should be avoided, as an audible S3 or S4 does not relate to the heart’s underlying electrical rhythm. Rapid ventricular filling generates the S3 (also known as S3, protodiastolic, or ventricular gallop). A presystolic gallop (also called S4 or atrial gallop) is heard just before S1 and occurs just after the P wave on the ECG. An audible S4 (dog or cat) is usually associated with increased ventricular concentric hypertrophy and stiffness. Rapid ventricular filling and atrial systole transpire very close together at rapid heart rates (common in cats), making differentiation between S3 and S4 impossible. The resulting single accentuated sound is referred to as a summation gallop.