An 81-year-old woman with a previous history of hyperthyroidism treated with 10 mg/day thiamazole presented with episodes of syncope. On admission, her ECG showed ectopic ventricular beats and a prolonged QT interval (QTc 520 ms). Torsades de pointes was recorded while she was having another syncope attack. A thyroid function test showed a thyroid-stimulating hormone (TSH) level of 72.7 AU/ml (range 0.3–4.0 AU/ml), free triiodothyronine (T3) 1.6 pg/ml (2.1–5.3 pg/ml) and free thyroxin (T4) 0.3 ng/dl (0.8–2.0 ng/dl), pointing to secondary hypothyroidism. We thought that this was the cause of her torsades de pointes and so we initially treated her intravenously with liothyronine 25 Ag/day and levothyroxine 50 Ag/day and subsequently orally with thyroxin 50 Ag/day, later increased to 75 Ag/day [1–5]. Our diagnosis was sustained by the absence of a long QT interval on a previous ECG while a thyroid test was slightly abnormal, with a shortened QT interval and the absence of recurrent tachyarrhythmias after thyroid replacement therapy. The arrhythmia never recurred and the patient’s QT interval returned to normal. We would