Hi there im 24, i started smoking weed a year ago. lately, i started to feel some pain at the left side of my chest i cant tell if its the heart?

From the posted information we can't either. At your age the more common cause of pain in that area is heartburn, since it is located at the stomach entrance, which is just to the left of and behind the heart.

Any time you ingest a foreign substance into your body some side effects can occur or if problems already there than the substance can exacerbate the existing condition. See a doctor if condition continues.

Using weed is not good for your health. Marijuana is a psychoactive drug and will mess with your brain. MJ users are called stoners for good reason. Quit using it while you are ahead.