This ECG demonstrates a narrow complex tachycardia having a rate if 178 beats per minute. It is from a 51 year old male who was admitted to the hospital with the chief complaint of chest pain and palpitations. There was no other evidence of heart disease. The QRS complex measures 0.10 sec (100 ms) and there is left axis deviation with a frontal plane axis of -68 degrees. No discrete P waves can be seen. This supraventricular tachycardia could be due to enhanced automaticity within the AV node or to re-entry within the AV junction in which case the retrograde P wave could be hidden within QRS complex.