The purpose of this volume is to evaluate the evidence concerning the cardiovascular reactivity hypothesis, which, in its simplest form, is that excess cardiovascular reactivity to psychological stress may constitute a risk factor for cardiovascular disease. This volume aims to further define, focus and refine this hypothesis by asking such questions as the following: What precisely do we mean when we speak of cardiovascular reactivity? What is properly considered excess reactivity? What is psychological stress? Is there a reliable relationship between stress and cardiovascular reactivity? What are the pathophysiological mechanisms that mediate the relationship between excess cardiovascular reactivity and its presumed endpoint, cardiovascular disease?