This 62-year-old man with a history of episodes of paroxysmal tachy-arrhythmias for several years is brought to the emergency department complaining of palpitation and dyspnea of 1 1/2 hrs duration:

•  Atrial tachycardia, 229/min
• Marked ST depression, consider subendocardial injury

The patient received diltiazem 25mg IV. ECG 2 is recorded 20 min later:

• Atrial tachycardia with 2:1 AV block
• Ventricular rate 112/min
• The ST segment is now normal

2 hours later the patient undergoes DC cardioversion:

• Sinus rhythm, 73/min.
• Non-specific T wave abnormality