system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Cardio gets the heart working which ultimately makes it stronger. So why do recreational drugs that do the same thing cause harm to the heart?

Shouldn't cocaine, for example, help improve the cardiovascular system?
gpt
when you exercise your whole cardio vascular (heart,lungs and arteries and veins) system adjusts to get more oxygen into your muscles, and also more waste out. 
All the components are working in tandem, increasing, decreasing and stabilising as required.   
Its a very nicely synced system

when you take cocaine its JUST your heart that increases. its now out of sync with rest of the system, even pushing against it and making your heart strain.
That's the problem.  

I suppose the cocaine case is a bit like having one formula-1 wheel on a car: its out of sync with the rest and you're gonna have a bad time.