Final answer:
Vasodilation in the heart and skeletal muscles during exercise is primarily due to sympathetic input on blood vessels and the release of acetylcholine and nitric oxide. This allows increased blood flow to active muscles.
Step-by-step explanation:
Vasodilation in the heart and skeletal muscles during exercise is primarily due to the effects of sympathetic input on blood vessels. Blood vessels in skeletal muscles are more likely to dilate, allowing increased blood flow to active muscles. Additionally, the release of acetylcholine and nitric oxide causes vasodilation in the brain and skeletal muscles.