The symptoms you are describing are usually referred to as palpitations--the sudden sensation of the heart speeding up or beating irregularly. Palpitations are relatively common, but it is important to determine whether they are being caused by something benign or whether they are a marker of a more severe underlying heart condition. For this reason it is best that you see your doctor
right away. Depending upon your prior health problems, he or she might want to refer you to a cardiologist.
In particular, it will be important to know if there are any patterns with these changes in your heartbeat. Do you notice this when you are exercising? When you are stressed? With a lot of caffeine? In addition, it is also important to know how long this sensation lasts for; whether it is accompanied by any other symptoms such as shortness of breath or lightheadedness; and then of course a physical exam with particular attention to the cardiac exam will also be a part of the evaluation. Your doctor will want to do an EKG
as a preliminary evaluation of the electrical system of your heart. In addition, depending upon your exam and history, you might be given a special monitor to wear at home to try and record your cardiac activity at home when you experience these palpitations.