Well, your heart rate will be elevated (as well as your blood pressure) while using an ECA stack. As far as long term side effects go, there are definitely some heart related issues linked back to using ECA, but there isn't enough research to suggest that it is really damaging. If you have a history of heart disease in your family then definitely stay away from this, otherwise it's probably going to do little damage as long as you stay within the standard dosing range..