The error is here: "These findings come from a study of 3,882 people who survived heart attacks."<quoted text>pot causes add when the mother is preg. and induces heart attacks in middle age men. Harvard http://news.harvard.edu/gazette/2000/03.02/ma...
To get the statistics right, you need to study a population of pot smokers and the proportion of heart attack in that population. Not a population of people having heart attack, and the proportion of pot smoker in it.
The next papers refer to that same study, and to another study where the statistics is done in the correct direction, but with too little samples.
Doing roller costers, or many sorts of sport, might still be much dangerous for the heart than smoking pot, taking the number they give.