Question

The two upper chambers of the heart are separated from each other by the

Answer 1

 lungs or ribs that separate the two upper chambers from each other

Answer 2

The upper chambers, called atria, are separated by the interatrial septum. The lower chambers, called ventricles, are separated by the inter ventricular septum. More generally these are called septa, or partitions. Ribs are outside of the heart, as are the lungs.