recently i have been having these very quick, sharp pains in my chest, more to the left side

feels like a little "shock", they don't last long, maybe a few seconds, but enough to make me wince, stop what i am doing. could this be sign of impending heart condition? this started to happen recently, and it doesn't happen every day. i am 42 and do smoke about 5-7 cigarettes - socially, once a week. i smoked on and off since my 20's but when i turned 40 i stopped smoking on a daily basis and managed to only smoke once a week. i have recently tried walking to get in shape since i have gained weight in the last year once i started taking 50 mg of zoloft per day. my weight normally was around 130. i am now 148 to 150 lbs. my eating habits are the same - i eat in moderation, probably could eat "healthier". i have been telling myself it is just my age causing the changes in the shape of my body - have more weight in my mid section.