The truth is that you're probably not going to find anything practically useful in this question. If you were to, say, overdose on Cocaine, you're going to experience a variety of other symptoms telling you that something is very wrong. Also, I'm not aware of any standards in place for Cocaine users dictating what an appropriate heart rate is while using Cocaine and/or how long said heart rate can last. The only tangible, useful information you can get here is to practice Harm Reduction when using Cocaine. If you suspect that something is wrong with your heart, then you need to seek medical attention.
Analysis of heart rate and such probably has value in some scientific sense, but for you, a casual user of Cocaine, you're not going to be left with anything you can actually apply to your situation easily. I respect what you're trying to do here, but the at-once un-scientific and also extremely scientific, we learn what we can tolerate with drugs by using them and experiencing them ourselves. You already know way more about how Cocaine effects you than anybody here could ever tell you, based on their own experience or their research.
For the record, cardiovascular events from Cocaine use often follow one of a few common trajectories
-Someone with an unknown, underlying heart condition uses Cocaine, has a heart attack and dies
-Someone overdoses by taking too much Cocaine, have a heart attack and die
-Someone develops long-lasting cardiovascular effects as a result of chronic Cocaine usage, but this doesn't become apparent until they die early, say in their early 50's from a heart attack or various other conditions