AbstractThe cases of two patients with hyperthyroidism and acute left ventricular (LV) dysfunction with segmental wall motion abnormalities resulting in heart failure are reported. Both had electrocardiographic changes mimicking ischemic coronary artery disease. Treatment with antithyroid medications, beta blockers, and angiotensin‐converting enzyme inhibitors rapidly restored LV function. The rapid reversibility suggests a role for myocardial stunning, an important entity to recognize in hyperthyroidism since this form of LV dysfunction can be reversed with appropriate treatment.