Ischaemic heart disease is the most common cause of heart failure, but less common causes such as hyperthyroidism should be kept in mind. As a potential reversible cause of cardiomyopathy hyperthyroidism should be excluded in every new patient, young and old, especially in the absence of coronary artery disease. Inspired by an intriguing clinical case we address the question whether hyperthyroidism-related cardiomyopathy is due to tachycardiomyopathy or to thyrotoxic cardiomyopathy.