Skipping beats
Fluttering rapidly
Beating too fast
Pounding
Flip-flopping
A Fever
Abnormal heart valves
Blood loss
Electrolyte abnormalities
Fear
Heart disease
Hormone changes associated with menstruation, pregnancy or menopause
Low levels of oxygen or carbon dioxide in the blood
Shock
Stimulants, including caffeine, nicotine, cocaine, amphetamines, and cold and cough medications that contain pseudoephedrine
Strenuous exercise
Stress
Too much or too little thyroid hormone
Cardiologist