OK, we probably ought to move this to medical, actually, and I shall do that momentarily. Weed smoking does indeed cause an "adrenergic" response in many people, especially within the first one or two hours of smoking. Despite everyone's calm assurances here to the contrary, that period of vaso-constriction, which seems to have to do both with the particular strain of weed and probably also with the diminished oxygen levels from smoking itself, raises the risk of heart attack by about five times what it normally is. The panicky, jittery response happens during this same period to people who have it. The paranoia, happens during this phase, too. These are well-documented, studied facts.
http://www.researchmatters.harvard.e...article_id=123

http://www.researchmatters.harvard.e...article_id=123

http://www.abc.net.au/science/news/stories/s107589.htm

Chances are, however, that if you have a healthy heart to begin with, a racing heart rate isn't going to cause anyone a heart attack or an explosion (which is almost impossible anyway). The people who're most at risk of having dangerous cardiac episodes after smoking--and there are certainly plenty of people who've actually died as a result of this, only they're counted as heart disease victims rather than cannabis-induced deaths--are folks with existing severe coronary artery disease.