Increasing evidence suggests overt and subclinical hyperthyroidism are associated with cardiovascular morbidity and mortality. This work prospectively investigated the hypothesis that poor outcome may be related to persisting cardiovascular abnormalities, particularly atrial fibrillation (AF). Cardiovascular symptoms, signs and haemodynamic disturbances were common in overt hyperthyroidism and persisted both during and after effective antithyroid therapy. AF was more prevalent in overt hyperthyroidism and persisted during and after effective antithyroid therapy. Cardiac autonomic function was abnormal in hyperthyroidism, persisting during treatment, but correcting after restoration of euthyroidism. An excess mortality was noted in the hyperthyroid cohort with presence of AF at recruitment, increasing age, male sex, and known vascular disease associated with it. Amiodarone induced hyperthyroidism (AIH) is a challenging condition. A retrospective study revealed use of thionamides alone was sufficient for successful outcome in the vast majority and differentiating between subtypes or discontinuing amiodarone had no influence on outcome.