My mom got heart attack, operation was not done, but she talks very less. It's been almost a month over. Is it because of the tablets she is taking?

Could be a lot of things, open heart surgery is not done just because someone has a heart attack. I would hope that the doctor gave you a reason as to why now be not the time to proceed with surgery; did they put in a stent? Maybe her arteries were not blocked enough to proceed and medicine could handle or fix any damage? Her slow speech could be from the possible new medicine she is on, I would contact her cardiologist ASAP and let them know about the changes and ask the side effects. Do not look it up on WebMD, call her physician, effects are different for every type of body, call her physician immediately.