When does the majority of pulmonary venous flow into the left atrium occur?

The majority of pulmonary venous flow into the left atrium occurs during early diastole. During this phase of the cardiac cycle, the heart is in a state of relaxation following contraction (systole), allowing the mitral valve to open. As pressure decreases in the left atrium, it creates a suction effect that draws blood from the pulmonary veins into the left atrium. This influx of blood corresponds with the phase when the left atrium is most compliant and able to receive blood effectively from the pulmonary circulation.

In early diastole, the left ventricular pressure is lower than the pressure in the pulmonary veins, facilitating this passive flow into the left atrium. This phase is critical for proper ventricular filling and overall cardiac output. Understanding the timing of pulmonary venous flow is essential for interpreting echocardiographic findings and assessing overall cardiac function.