A 75 year old woman was referred to our hospital for suspected sleep apnoea. Her medical history mentioned arterial hypertension and paroxysmal atrial fibrillation (AF). Polysomnography revealed obstructive sleep apnoea (OSA). During one phase of OSA the heart rate, determined by signals derived from pulse oximetry, showed a sharp rise in frequency (fig 1, left). Simultaneously recorded electrocardiography (ECG) indicated AF (fig 2A). The onset of AF was …