Cardiac arrhythmias are disorders of normal sinus heart rhythm caused by changes in the generation and/or conduction of electrical impulse and can classify them according to heart rate (bradyarrhythmias and tachyarrhythmias), QRS width (wide and narrow), regularity (regular and irregular) and origin (supraventricular and ventricular). They are a frequent reason for consultation in the emergency room, the most frequent is atrial fibrillation, and could become a life-threatening emergency that requires urgent action (especially if ventricular tachycardia and hemodynamic instability or poor clinical tolerance occurs). The most common symptoms include palpitations, dizziness and syncope but may be asymptomatic or lead to other symptoms. Initially we will evaluate the clinical and hemodynamic tolerance, we will have a 12-lead electrocardiogram (fundamental diagnostic tool in emergencies), analyzing in detail and systematic medical history and physical examination and request additional tests (analytical, chest radiography) seeking information suggesting the presence of structural heart disease and triggers or precipitating factors.