The heart is an organ that pumps blood around the body (so we can

stay alive) red blood cell  travels around the circulatory system. How the blood cells travel through the heart pumps. when you breath in air the blood cells go to the right atrium, through the tricucspid valve then the blood cells go through the right ventricle after the blood cells go thro`ugh the pulmonary valve then blood goes to the lungs to pick up some oxygen for the next drop off and the blood cells pick up co2  then to the lungs to get rid of the co2 through the left atrium, through the mitral valve to the right ventricle out the aortic valve.

Going up.  The blood cells are going the valves back to the heart.

Last but not lest we breath out the co2.