Caval opening

The caval opening is a hiatus in the diaphragm of humans through which passes the inferior vena cava, the wall of which is adherent to the margins of the opening, and some branches of the right phrenic nerve.

It is located approximately at the level of the eighth thoracic vertebra (T8), and passes through the diaphragm's central tendon.

It is quadrilateral in form, and is placed at the junction of the right and middle leaflets of the central tendon, so that its margins are tendinous.

By being situated in the tendinous part of the diaphragm, it is stretched open every time inspiration occurs.

Since thoracic pressure decreases upon inspiration and draws the caval blood upwards toward the right atrium, increasing the size of the opening allows more blood to return to the heart, maximizing the efficacy of lowered thoracic pressure returning blood to the heart.