Measurement of the left atrium size and function is a standard part of echocardiographic examination. Measurement of dimensions is now considered obsolete, the atrial area and volume are much more helpful to recognize its real size. Common methods used to measure the function of the left atrium include: pulse wave-flow Doppler measuring the transmitter flow, pulmonary veins flow and tissue Doppler imaging mitral anular velocities. The advanced methods to examine the function include the strain Doppler method, which calculates the atrial function from few local measurements in atrial walls and their subsequent averaging. Speckle tracking is an even more advanced method that enables calculating values from several locations – speckles. The main indication for transesophageal ultrasound is the left atrial appendage examination. We detect for the presence of thrombus, spontaneous echocontrast and examine its function, the lowering of which is a risk factor of thromboembolism.