system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it bad for your heart to take stimulants that increase your heart rate, but it is good for your heart to increase your heart rate through exercise?
gpt
what you typically want to do is decrease your resting heart rate, not increase it.

think of your heart like an engine: an engine that has been working tirelessly, for your whole life.  engines eventually wear out from too much use and wear, and from improper maintenance.  part of owning a car is that you *have* to use the car, because the car was designed to be in motion.

now imagine that you start the engine of your car, but you never actually put it into gear: it never leaves your driveway.  what you are effectively doing is using your engine but not using your car, same thing with taking stimulants to increase your heart rate but not actually exercising.  you are creating more wear and tear on your engine, thus limiting the life of your engine.

regular exercise makes your heart and your entire cardiovascular system more efficient, so more efficient cardiovascular = lower resting heart rate.  an inefficient cardiovascular system has several symptoms, and they vary from situation from situation, but overall, if your resting heart rate is high, that means your heart is working hard to overcome an inefficient cardiovascular system.  

hope this helps!