Palpitations are the sensation of feeling one's heart beating strongly. This can be due to any of a wide variety of causes ranging from anxiety to atrial fibrillation.

Worrying signs would include any association with shortness of breath, chest pain or palpitations at rest without any obvious causative emotional trigger. Medical advice should be sought if this is the case.

Pal`pi*ta"tion (?), n. [L. palpitatio: cf. F. palpitation.]

A rapid pulsation; a throbbing; esp., an abnormal, rapid beating of the heart as when excited by violent exertion, strong emotion, or by disease.

© Webster 1913.