Our understanding of the left atrium is growing, although there are many aspects that are still poorly understood. The left atrium size as an imaging biomarker has been consistently shown to be a powerful predictor of outcomes and of different cardiovascular disorders, such as, but not limited to, atrial fibrillation, congestive heart failure, mitral regurgitation and stroke. Left atrial function has been conventionally divided into three integrated phases: reservoir, conduit and booster-pump. The highly dynamic left atrium and its response to the stretch and secretion of atrial neuropeptides leaves the left atrium far from being a simple transport chamber. The aim of this review is to provide an understanding of the left atrial physiology and its relation to disorders within the heart.