Observations on Surgically Induced Insufficiency of the Canine Mitral Valve

SUMMARY Insufficiency of the mitral valve was produced surgically in 7 young male beagles. Clinical, radiological, haemodynamic, electrocardiographical and serum biochemical parameters were measured during the pre- and postoperative periods. Following post-mortem examination, lungs were examined histologically. Individual dogs were observed post-operatively for periods ranging from 1 to 20 weeks and on clinical, radiological and haemodynamic assessment could be divided into two groups. Group I showed marked passive pulmonary hypertension and an unusual pattern of exercise intolerance. Group II resembled clinical cases of mild left heart failure with compensation. Each group showed a definite sequence of cardiomegaly. A consistent feature was localized dilatation of the main pulmonary artery. Lung histology revealed mainly vascular congestion, with a relatively high incidence of inflammatory change.