The term supraventricular tachycardia (SVT) refers to atrial arrhythmias, including atrial fibrillation, atrioventricular nodal reentry, and atrioventricular reentry due to accessory pathway(s). In clinical practice, SVT may present as narrow- or wide-QRS tachycardias, and with the potential exception of atrial fibrillation, most of them are usually, although not invariably, manifest as regular rhythms. They are usually intrusive, symptomatic, and anxiety provoking but not dangerous. However, depending on their cycle length and the patient's background, they could also be, rarely, life-threatening conditions. In the acute setting, consideration of epidemiology data, clinical presentation, and the 12 lead ECG can provide diagnostic clues for differential diagnosis between SVT and ventricular arrhythmias, and guide appropriate therapy.