Canine Sick Sinus Syndrome

A grade 2/6 plateau-shaped systolic murmur (heard over the left apex), caused by mitral insufficiency, is auscultated in this heart sound.

A normal sinus rhythm is initially appreciated, followed by an abnormally prolonged pause. This pause is too long to be associated with a sinus arrhythmia and is consistent with a possible diagnosis of sick sinus syndrome in this patient.