Epinephrine and norepinephrine, in doses which cause little ectopic activity in unanesthetized normal dogs, produce exaggerated ectopic responses about the fourth day after coronary ligation, when the arrhythmias caused by the ligation per se have subsided. These responses persist for approximately 12 days after ligation and suggest reactivation of latent ectopic foci. Observations with methoxamine, isoproterenol, and atropine indicate that ventricular tachycardia is easily induced after occlusion by drugs which simultaneously stimulate the myocardium and slow the sinus node rate.