Heart palpitations are a series of rapid or irregular beats that can be scary—but they are not dangerous in and of themselves. Occasionally, however, they are caused by serious underlying medical problems, such as heart disease or hyperthyroidism (an overly active thyroid gland). That brief fluttering or pounding you feel in your chest when you speak in front of a group or when you narrowly avoid an accident is most likely benign anxiety-provoked palpitations. Other culprits include caffeine, exercise, stress, nicotine, cough and cold medications, asthma inhalers and some herbal supplements. If you have heart palpitations but no other suspicious symptoms, you're probably fine. But if you're in doubt, or you're experiencing dizziness, shortness of breath or chest pain, for instance, do see a doctor right away.