When your body is not used to being active , then starting an exercise suddenly without warm up can cause increased heart beat and heavy breathing.
Start an exercise programme slowly and build up gradually.
Do only as much as your body can comfortably handle without causing breathlessness, cramps or sprains.
Always warm up before exercise so that your pulse is raised slowly and cool down after exercise so that your pulse returns to normal slowly without causing any giddiness,
fainting etc.
Keep your body well-hydrated before and after exercise and do not exercise in a very hot or
cold enviroment.
Brisk walk is the safest form of exercise to begin with. Start with 5 minutes warm up that includes walking at a slow pace. Increase pace for next 5 minutes and then slow down again for 5 minutes to cool down after exercise. This makes it total 15 minutes of walk to begin with. Once you get used to it increase walking time by 5 minutes every week till you can walk for 30-45 minutes daily.
Do not walk beyond your comfort level. If you experience
chest discomfort, laboured breathing, or cramps, Stop exercising and rest till you feel normal.
Hope this will guide you better in starting an exercise program in a safe way.