Stress or anxiety
Strenuous activity
Extreme fatigue
Hormonal changes caused by pregnancy, menopause or menstruation
Low blood pressure
Caffeine
Nicotine
Alcohol
Stimulant medications, including pseudoephedrine (a decongestant)
Increasing age
Atrial Fibrillation
Cardiomyopathy
Hyperthyroidism
Heart valve disease
Other, more dangerous arrhythmias WPW Syndrome