Abstract
A 15-year-old Clydesdale cross gelding was investigated and managed over a 2-year period for intermittent collapse. The horse presented initially after an observed episode of collapse at rest, and had a resting tachycardia, elevated Cardiac Troponin I and polycythaemia. Multiple dysrhythmias were detected on telemetric electrocardiography. Vital parameters, cardiac rhythm and red cell count returned to reference range with prolonged rest but further resting syncopal episodes were observed, and due to safety concerns and limited treatment options the horse was euthanased. Post mortem evaluation identified extensive infiltration and replacement of right and left ventricular myocardial fibres with adipose and fibrous tissue, consistent with arrhythmogenic right ventricular cardiomyopathy. This report provides further information regarding the clinical and pathological features of this rarely reported condition.