4 min read • If you have a fast or irregular heartbeat, you may be suffering from a cardiac arrhythmia. Arrhythmias are fairly common, affecting an estimated 2.2 million Americans. While many arrhythmias are harmless, some can be life-threatening. If you think you may have an arrhythmia, it's important to see your doctor so he or she can diagnose and treat the condition if necessary. In the meantime, there are several things you can do to help your doctor get to the bottom of your symptoms. If you are at rest and your heart is beating faster than 100-120 beats per minute in a sustained manner, and you feel short of breath or dizzy, feel very anxious or close to losing consciousness, or have pain in your chest, go to the emergency room immediately. If you are alone, call the emergency line immediately.