In the sixteenth and seventeenth centuries, human physiology was mediated by the vital spirits. These fine vapors of heated blood and air not only linked body and soul, but were central to processes and ideas of generation, sight, mind-body unity, muscle and nerve action, and emotion. An ascending hierarchy of spirits rose from the liver, to the heart, up into the brain. This essay examines the distinctive role that bodily spirits played in Protestant religious experience, focusing especially on moments of particular interior drama. At a time when some Christians believed that the Spirit of God could fuse with these vital spirits in one's heart, the implications for “moments of grace” in Protestant piety are highly intriguing. The same can be said, mutatis mutandis, for moments when a “demonic” thought is suspected to have invaded the heart or brain.