I have met many smokers with diseases directly related to the habit of smoking cigarettes. I have never met a cannabis smoker in the same situation or that developed it over time (20 years span).
Obviously, cannabis smokers also die from heart diseases but if smoking cannabis was something that would be related to heart attacks we would know by now, a research would not be needed or it would be quite obvious and accepted.
Cannabis was illegal for many years in most countries (it often still is, but the laws are ignored). There have not been many studies year, given the timelines of the law enforcement I'd expect that we would first see the long term studies start to come out now. And of course the first studies will not be conclusive.
Obviously, cannabis smokers also die from heart diseases but if smoking cannabis was something that would be related to heart attacks we would know by now, a research would not be needed or it would be quite obvious and accepted.