Patients with tachyarrythmias as a result of thyroid storm have been typically treated with beta-blockers to decrease the heart rate and alleviate beta-receptor mediated symptoms such as anxiety and tremulousness. We report an unusual case of a previously well young man presenting to the emergency department with atrial flutter and who was clinically hyperthyroid. The patient was treated with propanolol to control his heart rate but suffered cardiovascular collapse. Although the patient was successfully resuscitated, he required inotropic support and intra-aortic balloon pump. The use of propanolol should be carefully considered in patients with thyrotoxic cardiomyopathy especially in those with heart failure because of the risk of exacerbation.