This paper illustrates a biological application of the concepts of relative change and area under a curve, from mathematics. We study two biological measures "relative change in cardiac output" and "cardiac output", which are predictors of heart blockages and other related ailments. Cardiac output refers to the quantity of blood pumped every minute by the heart. Determining the actual cardiac output of the heart requires invasive techniques and advanced mathematics. Fortunately, relative change in cardiac output can be easily determined by measuring blood pressure and heart rate of an individual first at rest and then after exercising. For completeness, a short discussion of the mathematical ideas used and a brief biological background are provided.