The technique of demonstrating the pumping mechanism of the heart was first shown in public in this TEDx Talk.
The detailed scientific description of the technique was published in the European journal, Science in School.
There is a beautiful app from Touch Press by Martin Clayton on Leonardo Da Vinci’s anatomical studies, explaining the difficulties he had trying to understand the heart.
This book by Thomas Wright describes the discovery of circulation by William Harvey, a hundred years after Leonardo Da Vinci. Harvey was also the first to prove that the heart is a pump, but he did it by lethal and gory demonstrations on live dogs. Many animals would have been saved if he had discovered this technique!