No drug is 100% safe. Asprin can kill. Shit, people die from eating peanuts.
That said, I've done a fair bit of, uh, research in the past. My experiments demonstrated that you don't really have to worry too much about your heart exploding. If the weed is really good you might THINK your heart is exploding, but it isn't.
The only advice I will give you is to make sure you are honest with yourself about whether or not the MJ is getting in the way of doing the things you want to do, especially when it comes to goals. I'm not saying it will, I'm just saying that it can.