The impetus for the mainstream media’s most recent fixation with the alleged dangers of pot is a French study, published online in the Journal of the American Heart Association. Investigators reviewed data collected by the French Addictovigilance Network, a national database of adverse case reports involving psychoactive substances, between the years 2006 to 2010.Apart from the fact that 60% of the subjects also smoked tobacco, according to Alternet:
Among the 9,936 total drug-related cases in the database, authors identified 35 cases (0.4 percent) in which both cardiovascular complications and cannabis were referenced.
...it is unclear whether these subjects used cannabis in the hours prior to any adverse event. Toxicological analyses identified THC, marijuana’s primary psychoactive compound, in only 13 of the 35 total cases. In the other 22 cases, no toxicology result was available; cannabis was simply referenced in the subjects’ medical file. In all but three cases, marijuana was referenced in conjunction with other substances, some of which are well associated with health risks, such as cocaine, alcohol, tobacco, and opiates.More detail in the original story (linked above).