What must occur during exercise to ensure adequate oxygen delivery to cardiac muscle?

A) An increased oxygen release to cardiac muscle
B) A decreased oxygen content to skeletal muscle
C) Decreased heart rate
D) Increased coronary blood flow

During exercise, the body needs more oxygen, especially in the muscles that are working harder, including the heart. To ensure adequate oxygen delivery to the cardiac muscle, there must be an increase in coronary blood flow. This allows more oxygenated blood to reach the heart muscle, supporting its increased activity during exercise.