Sick Sinus Syndrome

Sick sinus syndrome describes a pattern in which the heart's natural pacemaker — a small cluster of specialised cells in the right atrium called the sinus node — fails to generate electrical impulses consistently or at an appropriate rate. This can result in periods where the heart beats too slowly, pauses briefly, or alternates unpredictably between slow and fast rhythms. Owners often notice episodes of weakness, unsteadiness, or brief collapse, particularly during activity or excitement. Some animals appear quieter than usual, tire more easily on walks, or seem occasionally confused or distant. In many cases, these signs are intermittent and the animal appears entirely normal between episodes, which can make the pattern difficult to recognise at first. This page explores what sick sinus syndrome may look like in day-to-day life, the electrical and structural changes that underlie it, how the rhythm disturbance is identified and characterised, and the range of approaches used to manage it — from observation in mild cases to pacemaker implantation in others.