Trace the flow of Blood from the lungs to the heart?

Medical professionals can do this by injecting a radioactive isotope into the bloodstream and follow it's progress using imaging equipment (MRI for eg).

I can't think of way to do this at home.

If you wanted to check the blood supply to your foot, press your toe with your finger, once you have moved your finger, the area should look white briefly then go back to a pinky colour similar to the rest of your foot fairly quickly.