How are the cardiovascular system and the respiratory system dependent on each other?

Intricate connection. The respiratory system provides oxygen that nourishes the entire body, including the heart and vascular system. Without oxygen, we die. Without the left heart, oxygenated blood cannot be pumped through the body. De-oxygenated blood also has to get back to the lungs to be re-oxygenated. Receiving this blood from the vena cava, the right heart pumps it back through the lungs.