Left atrial volume is assessed by the biplane area-length method from apical 4- and 2-chamber views. The volumes are measured at end-systolic (just before mitral valve opening or the largest dimension), pre-atrial contraction (just before P wave), and end-diastolic (the smallest dimension or the onset of QRS complex), using the highest frame rate. The left atrial outlines at those three phases retrace off-line for three consecutive beats, then average. The recesses of the pulmonary veins and the left atrial appendage are excluded. The length of left atrium is that of the perpendicular line measured from the middle of the plane of the mitral annulus to the superior aspect of the left atrium. The left atrial volume is calculated as: 0.85 x 4-chamber area x 2-chamber area ÷ the shorter of the two lengths. The volume is indexed for body surface area. Left atrial distensibility is defined as: (end-systole left atrial volume - end-diastole left atrial volume) ÷ end-systole left atrial volume. Left atrial ejection fraction is calculated as: (pre-atrial contraction volume - end-diastole left atrial volume) ÷ pre-atrial contraction volume.