Cardiac arrhythmias, some of the most frequent diagnoses presenting at the emergency department, require a good and thorough understanding and quick recognition in the stressful emergency department environment. Despite dedicating significant time in training to the mechanisms and treatment of cardiac rhythm disturbances, most physicians are uncomfortable and lack confidence when faced with such clinical situations. Therefore, a solid understanding of the different causes and quick action is essential and can be lifesaving in the emergency room setting. Arrhythmias and conduction disorders are caused by abnormalities in the generation and/or conduction of electrical impulses in the heart. Symptoms such as dizziness, palpitations, and syncope are frequent complaints encountered by family physicians, internists, and cardiologists. In contrast to these ubiquitous complaints, which are generally benign, sudden cardiac death remains an important public health concern. Classification of arrhythmias is essential for the quick recognition and, thus, quick treatment. Currently, arrhythmias are divided simply as tachycardias and bradycardias. Bradycardias are further classified into heart block or simple bradycardia. Tachycardia, on the other hand, can be divided into two categories based on the width of the QRS complex: narrow complex (QRS duration is less than 120 milliseconds) or broad complex (QRS duration is more than 120 milliseconds). In 1970, Dr. Vaughn-Williams, Oxford University, introduced the first classification of anti-arrhythmic drugs. With regards to management of atrial fibrillation, Class I and III are used in rhythm control as medical cardioversion agents, while class II and IV are used as rate control agents.