Congenital cardiac disease in dogs.

Patent ductus arteriosus, aortic stenosis, ventricular septal defect, pulmonic stenosis and tetralogy of Fallot are the most frequently reported cardiac anomalies of dogs. Systolic murmurs occur after the first heart sound but before the second, while diastolic murmurs occur after the second heart sound. Murmurs associated with the pulmonic, aortic and mitral valves are best heard at the left intercostal spaces 3, 4 and 5, respectively, and those of the tricuspid valve at the right intercostal space 3 or 4. Mucosae at both ends of the animal should be examined for cyanosis. Right ventricular enlargement is characterized by a mean electrical axis greater than 100 degrees, a Q wave amplitude greater than 0.5 mv in leads II, III and AVF, and a positive T wave in lead V10. Left ventricular enlargement causes an axis of less than 40 degrees, a QRS complex duration greater than 0.06 seconds, an R wave amplitude greater than 3 mv, and a slurred or depressed ST segment. Atrial enlargement is characterized by a P wave duration greater than 0.04 seconds and a P wave amplitude greater than 0.4 mv. The cardiac silhouette is more upright and round on DV radiographs than on VD projections.