Our hearts beat all the time, however, ususally you do not feel it. Palpitation is the sensation that your feel your heart beat. It can be caused by skipped heart beat, irregular heart beat, or simply increased awareness of heart beat. If palpitation is infrequent and not associated with other symptoms, it is usually not serious. If palpitation is frequent, disburbing, and accompanied with other symptoms such as fainting, you should see your doctor.
By answering questions about your condition, you can find the causes.