The assessment of a patient with a tachycardia requires a systematic approach. First, the physician must determine whether the patient is experiencing evidence of hemodynamic compromise as a result of the tachycardia, which is generally not seen until the heart rate is greater than 150 beats per minute. Unstable tachycardias can be manifested by chest pain, shortness of breath, decreased urine output, mental status changes, or hypotension. Once a patient is noted to be hemodynamically unstable, the clinician then needs to assess the type of rhythm. This is important because the rhythm dictates what further management is needed. Generally, the rhythm is classified into two broad categories: narrow complex tachycardia or wide complex tachycardia.