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A 9-year-old 6.3-kg (13.9-lb) sexually intact male Maltese was referred to the Cardiology Unit of the Department of Veterinary Sciences of the University of Parma because of episodes of transient loss of consciousness (T-LOC) with vocalization, limb stiffness, opisthotonus, and urine incontinence. During the preceding few months, the T-LOC episodes became more frequent and occurred during both periods of rest and exercise. Physical examination findings were unremarkable except for a grade 1/6 midsystolic cardiac murmur, which was audible over the left apex, and an irregular cardiac rhythm. Echocardiography revealed mild left ventricular systolic dysfunction and trivial mitral valve regurgitation. During