I have recently begun walking briskly in order to get back in shape and after about five minutes of exercise my heart starts skipping beats frequently. It isn't just beating quickly, it is beating irregularly. It makes me nervous so I end up cutting my workout short which I don't want to do. Is this normal for someone out of shape? I am about 40 pounds overweight. Could this be a sign of a more serious condition? Any help would be appreciated!