The J wave, also known as Osborn wave, is a deflection that can be observed on the surface ECG as a late delta wave, seen at the end of the QRS complex. In this case, a 75-year-old woman, after 1 day of continuous haemodialysis, showed a marked hypothermia (28.5°C) and severe hypokalaemia (1.7 mEq/l). Bradycardia was seen on the monitor and J waves were recognised on the ECG recording. After appropriate replacement of potassium and treatment of hypothermia, the J waves disappeared spontaneously.Keywords J wave . Hypothermia . Hypokalaemia Hypothermia is generally defined as a core body temperature less than 35°C [1]. Hypothermia is classified as accidental or intentional and primary or secondary. Osborn waves are most commonly observed in hypothermia (hypothermic hump). However, some other conditions including hypercalcaemia, damage to the brain, cardiac arrest, Chagas disease, ischaemic heart disease and Brugada syndrome have been reported to cause J waves [2,3]. Below a temperature of 30°C, the J waves are detectable in 80% of patients [4]. Sinus bradycardia, prolonged PR and QT intervals or atrial fibrillation would be found in more profound hypothermia but all of these ECG abnormalities would normalise on re-warming [5]. Case reportA 75-year-old woman was admitted to our hospital with mechanical icterus and underwent percutaneous transhepatic cholangiography. There was no history of any cardiovascular disease. Electrocardiogram (ECG) on admission revealed normal sinus rhythm and left anterior hemiblock (Fig. 1). Haemodynamics were stable with a blood pressure of 120/70 mmHg and a heart rate of 88 beats/min. Physical examination was otherwise unremarkable. Unfortunately the patient's general condition deteriorated; she became anuric and she was intubated. Soon after intubation, haemodialysis was planned for the patient and after 1 day of continuous haemodialysis, the patient's body temperature was measured at 28.5°C and bradycardia was seen on the monitor. Figure 2 shows the patient's ECG recording at that time. Soon after the first recording, large QRS complexes were seen on the monitor and repeat ECG (Fig. 3) showed characteristic hypothermic humps, J waves, the QRS complexes became larger (200 msec) and the corrected QT interval reached 680 msec. A rightward axis shift was also seen. At that point a blood sample was taken and severe hypokalaemia (1.7 mEq/l) was observed. After appropriate treatment of hypothermia and hypokalaemia, the characteristic ECG findings disappeared, the main rhythm returned to normal sinus rhythm, the QRS narrowed (80 msec), and the corrected QT interval remained the same (680 msec). DiscussionThe J wave and elevated J point were described by Dr. John J. Osborn in 1953 [6], who worked on the use of hypothermia for cardiac surgery. The proposed cellular