At what point in the cardiac cycle is the left atrium at its greatest dimension?

The left atrium reaches its greatest dimension at the end of diastole. During this phase of the cardiac cycle, the heart is filling with blood in preparation for the next contraction. Specifically, the left atrial volume increases as it receives blood from the pulmonary veins, and this volume is maximized just before the left ventricle contracts.

Throughout diastole, the left atrium expands due to the influx of blood, and when the left ventricle is at rest and the mitral valve is open, the left atrium continuously receives blood. At the point of end diastole, any additional blood flow from the pulmonary circulation contributes to the maximum volume in the left atrium.

This understanding of the timing of filling is essential in echocardiography, as it helps in assessing left atrial size, which can be indicative of various cardiovascular conditions.