If you have shifted from a lighter job to a physically demanding job, your body and tour heart wouldn't be used to endurance training, so in the initial part you would feel the heart beating fast and other symptoms you describe, the best here is to go slowly with your job. Let the body get used to it. However if you feel breathless, chest heaviness, which is more when you are exerting and it persists more than one week, do visit a doctor for examination. Also avoid smoking during this period if you do. Regards Dr priyank mody