Figure 1.

Leftward movement of the interventricular septum. (a) Position of the interventricular septum during systole in normal conditions. (b) Dilatation of the right ventricle, which moves the septum over into the cavity of the left ventricle at the end of prolonged right systole. The pericardium surrounds the heart and does not allow excessive dilatation of the right ventricle without displacement of the interventricular septum. LV, left ventricle; P, pericardium; RV, right ventricle; S, septum.