A palpitation is an abnormal awareness of the beating of the heart, whether it is too slow, too fast, irregular, or at its normal frequency. The ifference between an abnormal awareness and a normal awareness is that the latter is almost always caused by a concentration on the beating of one's heart and the former interrupts other thoughts. Palpitations may be brought on by overexertion, adrenaline, alcohol, caffeine, disease (such as hyperthyroidism) or drugs, or as a symptom of panic disorder. More colloquially, it can also refer to a shaking motion. It can also happen in mitral stenosis.