no, it cant cause heart problems.... studies have shown that MJ actually stimulates the cardiovascular system

carcinogens, yes, any time you inhale smoke you will have them... but it isn't that bad for you. if you live in a major metro area, you inhale about a pack and a half (cigs) equivalent in carcinogens daily... nicotine is the prime cancer causing agent... w/o the nicotine, your lungs just expel all that nasty shit with little to no adverse health effects, highly variant on the individual ... your lungs can handle that shit easily, this is why everyone in the city doesn't get lung cancer :twocents:

overall, mj is pretty good for you, minus the burning plant matter part