If you always experience anxiety, most likely you'll develop fast heart beat as a consequence. Most of the manifestations brought about by anxiety have correlation with increased in blood pressure. To cite some symptoms are chest pain (angina pectoris), palpitations, tachycardia (rapid heart rate), and other related manifestations. These symptoms cannot be explained physiologically because it is related to anxiety rather than physical origin.
Having a rapid heart beat is a normal reaction to normal emotions such as fear or surprise; but for a patient suffering from anxiety, it can be a systematic reaction to just about any feeling. Feeling of anxiety can definitely affect the normal functioning of the heart, and every-time you are having anxiety attacks, your heart beats as if it's running in a marathon. In extreme cases, patients may even think they're about to have a heart attack and die. However heart attack will not likely happen because the adrenaline level is still not enough to cause cardiac arrest.
Once you've checked with your doctor and he has ruled out any all scenarios of heart problems, it will follow naturally that your racing heart is caused by nothing other than psychological anxiety. If you reach this conclusion, the most important thing you can do to get better is learning how to ignore your anxiousness. This is really not an easy task but it is attainable. Also, you need to always keep in mind that your reaction to any symptom of anxiety will contribute to making the symptom worse.
Remember: if you have an anxiety disorder, then anxiety is your actual problem - not the unpleasant sensations you may get from a racing heart or similar symptoms. Treating a symptom is never a definite way of treating its underlying condition. If you want to put an end to the disturbance you're experiencing from having a heart that's constantly racing for no reason, you have to focus on dealing with the disturbance, not the racing heart.
You might want to talk with a therapist to help you overcome your anxiety disorder, but there are also some new habits you may want to take up, that will help you deal with your anxiety yourself. Incorporating exercise in your regular routine can relax both your body and mind, and deep breathing exercises can help you calm in times of actual anxiety attacks.
Yoga or meditation, and jogging are helpful activities as well. Any exercise/activity that can divert one's attention from anxiety and can calm one's mind during attacks will do. Whatever you do, just remember that you need to break the cycle between your anxiety and your racing heart; worrying will only make you more anxious, which will in turn make your racing heart episodes more intense and frequent.
Once you're certain that it is anxiety that cause a rapid heart, then it would be easier for you to handle it. And dealing with it may actually be a lot simpler than you imagine. There are three important interventions that we should include in our daily activities - (1) decrease caffeine intake; (2) increased physical activity such as sports; and (3) practice deep breathing exercises. If you start following this advice, your problems will clearly vanish within a month.