Tachyarrhythmias and bradyarrhythmias are often seen in the outpatient setting. Patients can present minimally symptomatic or in extremis. Accurate diagnosis of the rhythm, plus a detailed clinical history, are critical for best management and optimal outcome. A 12-lead electrocardiogram is the cornerstone for diagnosis. Practitioners must identify patients who need immediate transport to an emergency department versus those who can safely wait for an outpatient specialty referral. This article reviews how to accurately diagnose and differentiate the most common tachyarrhythmias and bradyarrhythmias, the associated symptoms, and important concepts for the initial steps in the office management of such arrhythmias.