Moise N.S. and Dietze A.E.
Hyperthyroid cats were examined by electrocardiography, radiography, and echocardiography for the presence of cardiomegaly. These examinations were performed at the time of the initial diagnosis of hyperthyroidism and repeated during the course of antithyroid medication and after thyroidectomy was done. If the hyperthyroid cats had cardiomegaly, reduction in cardiac size was detected once the euthyroid state was reestablished. This decrease in size was appreciated electrocardiographically and radiographically. The echocardiogram demonstrated a decrease in left atrial size. A consistent decrease in left ventricular wall thickness was not observed by the echocardiogram, although 2 cats did have resolution of free wall hypertrophy.