Book excerpt: Heather Webb studies medieval notions of the heart to explore the "lost circulations" of an era when individual lives and bodies were defined by their extensions into the world rather than as self-perpetuating, self-limited entities. Drawing from the works of Dante, Catherine of Siena, Boccaccio, Aquinas, and Cavalcanti and other literary, philosophic, and scientific texts, she reveals medieval answers to such fundamental questions as: Where is life located? What does it consist of? Where does it begin? And how does it end? Against the modern idea of the isolated self, the medieval heart provides a model for rethinking the body's relationship to the world it inhabits.