Many things can cause palpitations. You may feel palpitations even when your heart is beating normally or somewhat faster than normal.
Most palpitations are harmless and often go away on their own. However, some palpitations are a sign of an actual heart problem. Sometimes, the cause of palpitations can't be found.
If you start having palpitations, see your doctor to have them checked.
Causes Not Related to Heart Problems
You may feel your heart pounding or racing during anxiety, fear, or stress. You also may have these feelings if you're having a panic attack.
Vigorous Physical Activity
Intense activity can make it feel as though your heart is beating too hard or fast, even though it's working normally. Intense activity also may cause an occasional premature (extra) heartbeat.
This answer from the National Heart, Lung and Blood Institute has been reviewed and/or edited by Dr. William D. Knopf.