Exercise represents a type of stress on the body. During exercise, body systems have to meet two challenges: one is to ensure continuous supply of energy for sustained activity and the other is to continuously remove metabolic end products generated during exercise. The cardiovascular and respiratory systems rise to this occasion by increasing their activities many fold. In this chapter, you will find changes in heart rate, oxygen uptake, stroke volume and cardiac output adequately explained. Redistribution of cardiac output during exercise is nicely depicted with the help of a diagram. Blood pressure responses to exercise are presented in a simplified manner. Respiratory changes during acute exercise are dealt with keeping the same policy- make it simple. In the process, a very popular myth viz. \'Decreased oxygen concentration or increased carbon dioxide concentration in blood is the stimulus for hyperventilation during exercise\' is busted. The chapter ends with explanation of another common query. \"Why sports anemia is considered a \"false anemia\"? After reading this chapter reader is in a position to convincingly tell why so much of importance is given to the heart as performance of cardiovascular system rather than respiratory system is a key factor in aerobic exercise.