If you ve had bypass surgery, then you must be careful to avoid too much exercise and strenuous activities. Too much of anything is bad and that goes for exercise too. It is advisable to do everything in moderation to derive benefits without causing any harm. So if on exercising, you have experienced chest pain, then it is a warning signal. If your pain subsides on resting, then it means your body is not able to bear that much of exercise. Listen to your body as it gives a warning sign before anything goes wrong. Climbing stairs can cause problem, so take steps slowly. Do not try to climb quickly. If angina persists or re-occurs, then you must visit a cardiologist. Excess exercise means exertion and exertion puts a strain on your heart. So, take care and be cautious next time. You can revert back to me for more clarifications, if you need any.