To The Most Serene and Most Puissant
King of Great Britain, France, and Ireland
Defender of the Faith
 MOST Serene King! The animal's heart is the basis of its life, its chief member, the sun of its microcosm; on the heart all its activity depends, from the heart all its liveliness and strength arise. Equally is the king the basis of his kingdoms, the sun of his microcosm, the heart of the state; from him all power arises and all grace stems. In offering your Majesty—in the fashion of the time— this account of the heart's movement, I have been encouraged by the fact that almost all our concepts of humanity are modelled on our knowledge of man himself, and several of our concepts of royalty on our knowledge of the heart. An understanding of his heart is thus of service to the king as being a very special portrayal, if on a more modest level, of his own functioning. Placed, best of Kings, as you are at the summit of human affairs, you will at least be able to contemplate simultaneously both the central organ of man's body and the likeness of your own royal power. Accept, therefore, I most humbly pray your most serene Majesty, with your accustomed goodwill and graciousness, this new account of the heart. For to you, who are yourself the new splendour of this age, and indeed its whole  heart, its central figure abounding in virtue and grace, we rightly refer whatever good obtains in this England of ours, whatever pleasure in our life within it.
Your most august Majesty's most devoted servant
To That Excellent and Distinguished Man
President of The London College of Physicians
and The Writer's Particular Friend
as Well as to The Other Learned Physicians,
His Most Kindly Colleagues,
the Writer's Very Warm Greetings!
 EXCELLENT Doctors! On several earlier occasions in my anatomical lectures I revealed my new concept of the heart's movement and function and of the blood's passage round the body. Having now, however, for more than nine years confirmed it in your presence by numerous ocular demonstrations, and having freed it from the objections of learned and skillful anatomists,, I have yielded to the repeated desire of all and the pressing request of some, and in this small book have published it for all to see. The booklet's appearance under your aegis, excellent Doctors, makes me more hopeful about the possibility of an unmarred and unscathed outcome for it. For from your number I can name very many reliable witnesses of almost all those observations which I use either to assemble the truth or to refute errors; you so instanced have seen my dissections and have been wont to be conspicuous in attendance upon, and in full agreement with, my ocular demonstrations of those things for the reasonable acceptance of which I here again most strongly press.
*Over many centuries a countless succession of distinguished and  learned men had followed and illumined a particular line of thought, and this book of mine was the only one to oppose tradition and to assert that the blood travelled along a previously unrecognized circular pathway of its own. So I was very much afraid of a charge of over-presumptuousness should I have let that book, in other respects completed some years earlier, either be published at home or go overseas for printing unless I had first put my thesis before you and confirmed it by visual demonstration, replied to your doubts and objections, and received your distinguished President's vote in favour. If, however, I have successfully maintained my thesis with you and our College, distinguished as it is by learned men of such number and greatness, then I am quite sure that I have less to fear from others; nay, even that which came from you, because of your love of truth, to provide my sole comfort will come also, I hope, from all others possessing a similar philosophy.
*For true Philosophers, aflame with love of truth and wisdom, never find themselves so sage or so full of wisdom or so abounding in perception but that they cede place to truth from whomsoever or whensoever it comes. Nor are they so narrowminded as to believe that our forebears have passed on to us any skill or knowledge so complete in all respects and perfect that nothing is left for the industry and diligence of others to accomplish. Very many, indeed, profess that the things we know are negligible in amount compared with those we know not. And Philosophers suffer not themselves to become enslaved and lose their freedom in bondage to the traditions and precepts of any, except their own eyes convince them.
*Nor, while swearing allegiance to Mistress Antiquity, do they openly abandon Friend Truth and desert her in sight of all. But, while regarding as credulous and empty those who accept and  believe all at first glance, equally do they regard as dull and senseless those who do not see the things that are manifest to the sense, or acknowledge day-time by the light of noon. Hence their teaching is to reject equally, in their course of training, on the one hand the poet's tales and the rabble's absurdities and on the other the suspensions of judgment of the Sceptics.
*Again, studious, good and honest men as a whole never let their mind be so overwhelmed by feelings of indignation and envy as to prevent them from giving a fair hearing to proposals made on behalf of truth, or from understanding what is demonstrated to them. Nor do they think it degrading to alter their view if truth and a public demonstration so persuade them, or regard it as dishonest to desert errors, albeit most venerable ones. For they know very well that it lies within all men to err and to be deluded, and that many discoveries have been made through the chance learning of one person from another, of an old man from a young man, of a keen-witted one from a foolish one.
It was, however, dear Colleagues, no intention of mine, in listings and upturnings of names, works and views of anatomical authors and writers, to make display by this book of my memory, studies, much reading, and a large printed tome. In the first place, because I profess to learn and teach anatomy not from books but from dissections, not from the tenets of Philosophers but from the fabric of Nature. Secondly, because I consider it neither fair nor worth the effort to defraud a predecessor of the honour due to him, or to provoke a contemporary. Nor do I think it honourable to attack or fight those who excelled in Anatomy and were my own teachers. Further, I would not willingly charge with falsehood any searcher after truth, or besmirch any man with a stigma of error.  But without ceasing I follow truth only, and devote all my effort and time to being able to contribute something pleasing to good men and appropriate to learned ones, and of service to literature.
Farewell, Excellent Doctors, and look with favour upon your Anatomist
Source:William Harvey (1628). The Movement of the Heart and Blood, in The Circulation of the Blood and Other Writings, tr. Kenneth J. Franklin (London: J. M. Dent and Sons, 1963).
Note: a long paragraph in the above text has been broken up in this excerpt into smaller ones for purposes of ease of reading. The paragraphs marked with an asterisk "*" are all part of the preceding paragraph.