system
Given the following post, respond as if you're commenting on Reddit:
human
Why is elevating your heart rate through exercise good for your heart but elevating you heart rate with caffeine bad for it?
gpt
Elevating your heart rate through exercise causes your vascular system to dilate, allowing for greater bloodflow. When the veins are wide open, the heart does not need to work as hard to pump more blood.  However, caffeine is a vascular constrictor, causing your heart to work harder to pump the same amount of blood.  Coupled with an elevated heart rate, your heart is now trying harder to force blood through constricted passages, which puts undue strain on your heart and your vascular system.