Acquired atrial septal defects secondary to rupture of the atrial septum in dogs with degenerative mitral valve disease

Acquired atrial septal defects (ASDs) secondary to atrial septal rupture are uncommon in dogs with degenerative mitral valve disease. Echocardiographic diagnosis of these defects has not previously been described. The echocardiographic features in two cases identified antemortem are presented in this report. ASDs can be difficult to identify on two-dimensional echocardiogram when relatively small in size and may be underreported. Acquired ASDs may alter the physiology, treatment plan and prognostic implications for the dogs in which they occur and their presence should be considered in all cases of degenerative mitral valve disease that develop signs of right-sided heart failure.