text: if the heart rate directly affects co what affects the heart rate?   the faster the pulse rate the more chemical exchange of oxygen and co2. thus, the faster your heart beats the more blood it's pumping and therefor the more need for oxygen and co2.    physical activity or emotional stress are usually the two leading causes for an increase heart rate, and in your question, oxygen and carbon dioxide are increased to keep up with the demand of the heart. so really the respiratory system is adjacent to the cardiovascular system.