In book III, chapter 8 Riolan discusses the heart and presents his views on the circulation of the blood. "Riolan's opinion of the blood movement seems to have arisen from his attempt to reconcile strict Galenic belief with Harvey's theory of the circulation. The resulting inconsistences and contradictions Harvey was not slow to point out. Indeed, so little of either truth or sense is there in the whole passage, that one can only admire Harvey's patience and his reply. What is abundantly clear from the passage is that Riolan is theorizing without looking, and his theorizing is dictated by his passionate desire to see the medicine of Galen kept intact and his fear lest Harvey's doctrine overturn its foundations" (Whitteridge). "The significance of the volume is that it stimulated William Harvey to extend his experiments and to publish a detailed critique of Riolan's work. Whitteridge summarizes the content of Harvey's first letter (published in Cambridge, England, in 1649)....She indicated that Harvey had two goals: 'To refute Riolan on every point and to show that his own doctrine of the total circulation of the blood does not destroy the ancient physic but further[s] it. Whitteridge goes on to explain that the second letter from Harvey to Riolan 'partakes of a totally different character from the first'. She continues, 'The greater part of Harvey's Second Letter is a restatement of his hypothesis concerning the circulation of the blood, supported by further experimental proof" (W. Bruce Fye). Whitteridge, William Harvey and the circulation of the blood (New York, 1971).

Translated into English as A sure guide, or, The best and nearest way to physick and chyrurgery that is to say, the arts of healing by medicine and manual operation : being an anatomical description of the whol body of man and its parts : with their respective diseases demonstrated from the fabrick and vse of the said parts : in six books ... at the end of the six books, are added twenty four tables, cut in brass, containing one hundred eighty four figures, with an explanation of them : which are referred to in above a thousand places in the books for the help of young artists / written in Latine by Johannes Riolanus ...; Englished by Nich. Culpeper ... and W.R. ...London: Printed by peter Cole, 1657. Digital text available from Early English Books Online at this link