In the near future, artificial hearts may be quite different from natural hearts. The pulse and variable speed of the human heart are difficult to reproduce in reliable machines, and they might also be inessential to the heart's main function, moving blood. So these devices will not reproduce them. Instead, they will provide a constant flow of blood. There is no need to be sentimental about this. We know that what is essential to being who we are resides no more in the heart than it does in the liver or any other mythological seat of the self. Still, what would it be like to have such a heart and be really angry? Anger clearly is a conscious state, of course, but a change in blood pressure and a pounding heart seem to be important parts of it. Is there any sense in which a person with a heart that provides a constant flow of blood could experience what we do when we are angry? Spinoza's account of the passions is one of the most immediately engaging parts of his account of the human being because it captures the intimacy of the physical and the psychological in passion. So many of our passions are, like anger, clearly psychophysical that something like Spinoza's identification of mental and physical states, a position often seen in other contexts as a liability of the Ethics, seems practically required of a good account of the passions. This essay describes Spinoza's theory of the passions in the Ethics and focuses on the details of Spinoza's accounts of the mental and physical aspects of passion and on the ways in which those accounts correspond to each other.