Left atrial evaluation is strongly linked to the history of cardiac imaging. In the past, the importance of this chamber has been largely downplayed because cineangiography could not visualize it directly. Nowadays echocardiography can easily assess left and right atrial size and function. Left atrial enlargement is frequent in many cardiac diseases. A main determinant of left atrial volume is ventricular diastolic function. It has recently been suggested that left atrial volume might be the morphophysiologic expression of chronic diastolic function. In fact the left atrium is exposed directly to left ventricular diastolic pressure through the open mitral valve and because of its thin wall structure it tends to dilate with increasing pressure. Other important determinants of atrial volume are the degree of ventricular remodeling, mitral regurgitation and the presence of atrial fibrillation. The degree of left atrial enlargement is associated with adverse prognosis in different clinical settings. Patients with dilated cardiomyopathy and with a left atrial volume > 68 ml/m2 have a 3.8-fold risk compared with those with smaller left atrial volume. The predictive value of left atrial volume is independent of left ventricular systolic and diastolic function, mitral regurgitation and atrial fibrillation. This is noteworthy because these factors are both determinant of left atrial volume and have a strong impact on outcome. It might be concluded that left atrial volume represents a powerful predictive marker because it is a window allowing comprehensive evaluation of several factors associated with bad prognosis, which are often difficult to document separately.