What does the heart pump besides oxygen-rich blood?

Answer 1

The heart pumps blood, and also the plasma that, with the blood cells, make up the volume of the circulatory system. The red blood cells dump carbon dioxide (CO2, which they picked up from the cells of the body) in the lungs, and pick up oxygen (O2) there. The oxygen is carried to the cells and exchanged there for the carbon dioxide. (The cells need the O2 and excrete the CO2.) There's a bit more.

The blood also contains the plasma, which carries the nutrients the cells of the body need. The nutrients are collected from the digestive system and carried in the plasma. That plasma also carries the waste products of the cells to the liver and kidneys so it can be "pulled out" and disposed of.