Homeostatic+Relationship

Homeostatis: physiological process by which the internal systems of the body are maintained at equillibrium

So, a homeostatic relationship is a relationship in which things (in this case, two organ systems) rely in each other to maintain a balance.

The lungs depend on the heart to circulate the blood to cells, and bring blood to the lungs to carbon dioxide can be removed. The heart depends on the lungs because the heart is made up of cells, and all cells require the nourishment of oxygen.

Neither one of these processes could occur without both organ systems working properly.