Structure of the left atrium

Generally conceived as a simple structure, the left atrium can be considere d in terms of three components: the appendage, the venous compartment and t he vestibule. A fourth component, the septum, is shared with the right atri um. The myoarchitecture of its wall is more complex than suggested by its r elatively smooth appearance. The subepicardial and subendocardial fibres ar e aligned differently. There is a general pattern of fibre arrangement but regional variations an common. Sleeve-like extensions of myocardial fibres into the pulmonary veins are most extensive in the upper veins. The structu re of the left atrium is complex and closer examination can aid in understa nding atrial function.