Chronic atrial fibrillation is a persistent cardiac arrhythmia characterised by disorganised atrial electrical activity leading to an irregularly irregular ventricular response lasting longer than 12 months or requiring ongoing treatment. It matters clinically because it increases the risk of stroke and heart failure, necessitating long-term anticoagulation and rate or rhythm control strategies. A key complication is thromboembolism, particularly ischaemic stroke, due to atrial blood stasis and clot formation.