How to make working model of …

The heart is a muscular organ that  pumps blood to different parts of the body through blood vessels.  The human heart has 4 chambers: 2 atria and 2 ventricles. The atria are used to receive blood from the body and the ventricles pump blood to the body.  The heart and the blood vessels are part of the circulatory system, which sends blood around and around your body in one direction.  Your heart has valves that allow blood to move forward but prevent it from moving backwards.
Your heart works alongside your lungs.  Every time you breathe, you use your lungs.  The lungs are soft, sponge-like organs that expand when filled with air, like a balloon.  As you breathe in, your lungs take in oxygen which our blood picks up.  This goes to the heart, which then pumps the oxygen-rich blood through your body for your cells to use.  Once your cells use the oxygen, they release carbon dioxide back into the blood.  This blood goes back to the heart, where it is pumped to the lungs, which then breathe out the carbon dioxide gas.  Then your blood picks up more oxygen and the cycle continues.
In our heart model, the cup is your heart, the pressing motion from your finger on the balloon is the pumping muscle, the water is your blood, the straw with the balloon on it is the atrial valve that keeps "blood" from pumping out in the wrong direction, and the other, open-ended straw is the ventricle through which the "blood" flows.