John Milton, George Herbert, and John Donne all struggle to hold onto the heart as the center of man and the place of inspiration and volition. In the seventeenth century, four intertwined challenges to how people think about the heart collide. In anatomy, Harvey's treatise On the Motion of the Heart and the Blood (1628) persuaded many people to think of the heart as a mere pump rather than a mysterious seat of knowledge and volition. Milton, Herbert, and Donne respond to this controversial shift and work to realign the heart with the mystical presence of God. In philosophy, Descartes's theory of dualism changed how people thought of the connection between the heart and the mind. Milton confronts Descartes's dualistic theories by upholding monism in his epic Paradise Lost and portraying his archfiend, Satan, as a dualistic philosopher. In economics, anxieties concerning the mass-production of books complicated the Judeo-Christian belief that God writes on individual hearts in a personal, non-manufactured way. Herbert chooses to avoid mass-producing his works during his life due to his fear that "copying out" the writing in his heart would be diluted through the printing process. Milton, however, chooses to use the vehicle of print to advance his belief that the most lasting monuments are inscriptions written by God in hearts. In theology, the impassioned controversy about the interiority versus outward signs of belief that erupted in the sixteenth century continues to be debated in the seventeenth century and affects how these theological poets conceptualize the heart. Herbert and Donne characterize the heart as an intimate sphere that God must personally break and appropriate, whereas Milton demonstrates in "The Passion" that the crucifixion of Christ is a distinct and revered topic that cannot be expressed on physical paper but must be completed by the Spirit of God inside each believer's fleshy heart. This project shows how Milton, Herbert, and Donne reinforce the presence of God working and writing in believers' hearts when the very nature and understanding of the heart is evolving and moving away from any connection with the divine.