Unmasking of left heart dilation following treatment for precapillary pulmonary hypertension.

A 13-year-old spayed female dog was referred for a history of tachypnea and dyspnea. Severe pulmonary hypertension was diagnosed based on tricuspid regurgitation velocities and 2-dimensional echocardiography. Left atrial size was normal at the time of this diagnosis. However, following treatment with a selective phosphodiesterase inhibitor, echocardiography revealed unmasking of left heart dilation. Key clinical message: If phosphodiesterase inhibition therapy is deemed appropriate in patients with hemodynamically important myxomatous mitral valvular disease, using the lowest effective dosage and careful monitoring with echocardiography ± thoracic radiographs should be considered.