Hi.. Palpitation can occur due to physiological cause such as stress, anxiety and other psychogenic factors.. They could also be seen due to certain drugs such as triamterene (which can cause irregular pulse) that you have been, and other factors such as infection, anemia and other endocrine dysfunctions... Since your heart evaluation were normal it is unlikely to be due to heart problem, though there are chances that a repeat evaluation can show abnormalities..

This is just for information purpose.. What may be the cause for palpitation to occur can be found only by an examination by a doctor...

Well what is suggestive is that since its been a year you got yourself examined,you can have a physical evaluation done by a Cardiologist which is better than self medication considering its our Heart.