Weed has stimulant-like effects on the heart.
It has depressant-like effects on coordination (in many cases, but not all) and the CNS.
Smoking weed does not increase the desire to try harder drugs. Weed is THE gateway drug. It is also the most readily available and used illegal drug I know of. Obviously the fucking anti-drug programs will label that as meaning weed is the gateway drug, but it is only so due to obvious, inherent factors. If you started out with cocaine, you'd get into weed afterwards. Does that make cocaine the gateway drug to weed?
Felon, weed induced psychosis is something I have never seen in my life, nor have I ever heard of it, despite plenty of reading and hands-on work on the subject.
When you inhale, in general, I believe your heart rate increases slightly.
When you inhale any smoke (as far as I know), your air passages constrict. This could cause an increased heart rate as well (aside from the direct effect weed has on heart rate).
Some cannabinoids have been linked to heart failure in a small amount of cases. These were synthetic. They were part of a host of drugs.
---------- Post added at 06:40 PM ---------- Previous post was at 06:06 PM ----------
Also, depening on how you roll that blunt, you could get some nicotine. In fact, some blunt wraps are nicotized. Nicotine, when inhaled, causes that feeling of constriction on your airways and increases your heartrate within 10 seconds.