An S3 gallop sound is heard in this heart sound; a murmur is present but is difficult to appreciate. The third and fourth heart sounds occur during diastole and are not normally audible in normal dogs.
An S3 heart sound is lower in frequency than S1 and S2 sounds, and it is usually best heard with the stethoscope bell. An S3 sound may sound like the galloping of a horse, hence the term gallop heart sound. The term gallop rhythm should be avoided, as the presence of an audible S3 sound does not relate to the heart’s underlying electrical rhythm. Rapid ventricular filling generates the S3 (also known as S3, protodiastolic, or ventricular gallop). An audible S3 is commonly heard with diastolic volume overloading, as in this patient with severe mitral insufficiency.