Atrial fibrillation (AF) affects as many as 1 in 16 people over the age of 65 and reduces the quality of life of large numbers of people in the UK and around the world. Catheter ablation is a minimally invasive treatment that has been developed to help eliminate AF. Recent studies have identified that a particular area of the heart, namely the left atrial appendage (LAA), which is a pouch in the left atrium (small collecting chamber of the heart), may be the main source of AF in many cases. There is a clear lack of knowledge about the structure, anatomy, function and electrical properties of the LAA, which is fundamental to furthering our understanding and management of AF.