The acute dangers are often underestimated. The degree of vessel contriction caused by cocaine on the coronary arteries is tremedous ! (another adjective !!) It is capable of causing full thickness infarcts even when no evidence of atheroma is found (from autopsy studies). That is it can reduce the diameter of the vessel literally to zero and for several minutes!
Vasoconstriction with cocaine will cause ischaemia which can be reversible or irreversible (infarction) or incomplete as in Non-STEMI. Therefore there can be microscopic damage to the myocytes. If this occurs at a time of increased oxygen need by the heart (ie with cocaine, and secondary noradrenaline effects) where increased contractility is required and increased force of contraction, then there is an oxygen supply : demand debt, and damage occurs. This can lead to myocardial fibrosis and reduces the compliance of the LV.
Take the super fit athlete with a HR of 40 - the reason why his/her heart only beats 40 times per minute is that the body's cardiac output demand can be achieved with a lower rate (and hence a greater stroke volume). Lower resting heart rates are very efficient in terms of 'power' - energy used per work done.
With stimulant use, the oxygen supply is impeded, and the afterload is much greater. Hence the stroke volume is reduced and the efficiency of the system is lost.
Even though with training you get increased vessel density throughout muscles (including the heart) - they are maximally open with exercise by tissue autoregulation to allow maximum delivery of oxygen. With stimulant use, any additional vessels (unsure if any do develop - suspect not) - will be vasoconstricted which will subtract from the effect of autoregulation.
http://www.bluelight.ru/cgi/ultimatebb1.cgi?ubb=get_topic&f=15&t=004487&p=
The great heart effects question! (beta/alpha antagonism)
Stimulant drugs do not mimic many of the (healthy) effects of exercise, so it's innacurate to assess the dangers of a drug by how much your heart rate or blood pressure increase. And in the case of cocaine, it causes a degree of vasoconstriction greater than any other stimulant and greater than any type of exercise. And vasoconstriction is what leads to a myocardial infarction (heart attack, a coronary artery so constricted that blood/oxygen cannot reach part of the heart), not merely a high heartrate.