In general practice palpitations are reported in around 8 per 1,000 persons per year. The differential diagnosis includes cardiac and psychiatric causes, as well as numerous others e.g. anaemia, hyperthyroidism, prescribed medication, caffeine and recreational drugs. Factors that point towards a cardiac aetiology are male sex, irregular heartbeat, history of heart disease, event duration > 5 minutes, frequent palpitations, and palpitations which occur at work or disturb sleep. Other clues suggesting a cardiac origin are abrupt onset and termination of palpitations, positional palpitations, and accompanying symptoms such as dizziness and presyncope. Cardiac arrhythmias are the result of enhanced automaticity, triggered activity or re-entry. The latter mechanism is responsible for the majority of clinically relevant arrhythmias, such as atrial fibrillation and supraventricular tachycardias. The prevalence of supraventricular tachycardia in the general population is around 2-3 per 1,000 persons. AV nodal re-entry tachycardia (AVNRT) is the most common paroxysmal supraventricular tachycardia, accounting for nearly two-thirds of all cases. The typical clinical presentation of AVNRT is a sudden onset of palpitations (98%) and/or dizziness (78%). Patients may present at any age and are more frequently female than male.