This article concerns the notion of living bodies that Spinoza develops in the Ethics (published posthumously in 1677). While commentators have emphasized the relevance of Spinoza’s works for contemporary physiology, they have neglected to study Spinoza’s own views on this topic. My aim is to draw attention to the specific parti pris that underlies Spinoza’s passages on anatomy. To do so, I first compare Spinoza’s claims on human body with the conceptions developed in his immediate historical environment. Then, I propose to draw a parallel between Lakatos’s notion of “negative heuristics” and the high level of generalization Spinoza demonstrates in his propositions on the human body. This parallel allows me to show how Spinoza’s critical remarks on our knowledge of human body have heuristic value.