Palpitations are an awareness of your own heartbeat, usually because the heartbeat seems irregular, or unusually rapid, or in some other way "different" to normal. An abnormal heart rhythm is referred to as an arrhythmia
Normally, of course, you are not aware of your heart beating at all. The heart beats in response to an electrical stimulus (a bit like the way a car engine fires in response to a spark from a spark plug), and palpitations usually stem from a problem in this electrical system that generates the heartbeat. The heart muscle can continue to contract effectively even if the electrical system is "misfiring" from time to time.
The first thing to emphasise about palpitations is that they usually do not mean that you have a significant heart problem, and in many cases do not even require treatment, although just occasionally they can be an indicator of a potentially serious condition. Even if treatment is required, the cure may be quite simple, such as avoiding caffeine (coffee, tea, coca cola), avoiding drugs which can make the heart race e.g. decongestants and cold
cures, or avoiding excessive alcohol use.
Often you may not be aware of anything apart from the abnormal heart rhythm itself, but palpitations can be associated with other things such as tightness in the chest, shortness of breath
or light-headedness. Depending on the type of rhythm problem, these symptoms may be just momentary or more prolonged. Actual blackouts or near blackouts, associated with palpitations, should be taken seriously because they often indicate the presence of important underlying heart disease