I am sufring from body problem. i am quickly tired on walking and my heart rate increase rapidly.

Internal Medicine: Based on the limited information provided the symptoms are: easy fatigability and tachycardia, possibly tachy-arrythmia brought on with minimal exertion. Many medical conditions can cause these symptoms, some benign and easily treatable. However, a detailed history and exam by your doctor along with at least a chest x-ray and an ECG is needed to rule out some of the more concerning medical causes.

See a doctor, soon: Having these symptoms at age 21 is very concerning. It might be as simple as being overweight and out of shape or it could mean a problem with your heart or lungs. You need to be evaluated by a physician. Whether it is just a matter of being "out of shape", or a more serious problem, your doctor will help you evaluate and treat the problem.