The scientific work of Leonardo da Vinci may have served as the main inspiration for the historical research of George Sarton. Although he never produced a work he felt was worthy of its subject, the little that he did write about Leonardo reveals the importance he attributed to him in the history of science. This is especially clear in Sarton´s treatment of Leonardo and a discovery he did not make: William Harvey´s discovery of blood circulation in the 17th Century. In (...) this article, we refer to this particular episode to trace Sarton´s conception of the development of science. It is a conception that illustrates well the traditional historiographic perspective that is the target of Thomas Kuhn´s criticisms. Although Kuhn never wrote about Leonardo or Harvey, we aim to show that he clearly positioned himself contrary to Sarton, albeit indirectly, with respect to this particular historical episode, as well. (shrink)