The ventricular septal defect is an anomaly linked to genetics in some dog breeds, where an abnormal communication between the ventricles is kept allowing blood flow between ventricles. The magnitude and direction of communication depend on the size of the hole and the relative resistances in the pulmonary and systemic circulations. The report describes a clinical case of a male Fox Terrier, 20 months old that showed cyanotic mucous membranes and abnormal heart sound on auscultation. The echocardiography revealed a ventricular septal defect and hypertrophy of both ventricles.