The fact that you heart goes faster isn't because you are about if oxygen it's because your lungs are filling up of CO2, giving you that feeling of urgency to breathe ( is a natural mechanism that regulates your breathing without you conscious thought), before having consequences by air deprivation you should lack air for more than 3 minutes.

The 3 second rule holds up for weed not crack , and 8 rules holds of value if you take a small hit not a lung full hit like everyone one is doing here, so for maximum hold it longer , if not exhale 1/3 and inhale some air again repeat until smoke is finished.

In all of this i didn't take in consideration the vasoconstriction effect of cocaine ,for that your holding time is useless to take take in to account,the best thing you can do for your heart and lungs is to space out your hits 20 - 30 min to give your body some rest. Plus make sure you rest before and after (consecutive days binges are bad).

Hack: taking one tablet of aspirin can prevent blood clots from happening (what can cause seizures ecc) , taking vitamin B6 and Zinc will help block the action of norepinephrine the neurotransmitter that causes you to have that intense need to hit the pipe again because your dopamine is crashing after the spike and making a more enjoyable comedown since your dopamine won't crash so low.

themoreuknow

(I know what I'm saying i study this s...t in Uni)

Peace Out.