Atrial tachycardia resistant to conventional management may respond to ivabradine. Two cases of resistant tachycardia are presented that responded to ivabradine. Both cases were later successfully ablated and both maintained sinus rhythm and are symptom free 2 years post procedure. The physiological mechanism for this is also briefly discussed. KEYWORDS Atrial tachycardia; Ivabradine Case 1In 2009, a 27-year-old male was referred to our arrhythmia clinic with palpitations. His heart rate (HR) was up to 140 b.p.m., based on electrocardiogram and exclusion of other causes of sinus tachycardia, an initial diagnosis of inappropriate sinus tachycardia (IST) was made. The echocardiogram showed a reduced (25%) left ventricular ejection fraction (LVEF), suggesting tachycardia-induced cardiomyopathy. The first attempt to control HR was with b-blockers and amiodarone, but it was only partially successful. The ivabradine dose was titrated to 7.5 mg twice daily and then a normalization of HR was obtained (i.e. 65 b.p.m.). The echocardiogram also showed normalized LVEF with an EF of 55%. Two years later, in 2011, ivabradine was stopped by his cardiologist. The patient once again developed tachycardia-induced cardiomyopathy (EF of 40%). He was then started on amiodarone (400 mg daily), which failed to control HR and to improve cardiac function. Ivabradine 7.5 mg twice daily was then resumed and after 6 months HR was stabilized at 70 b.p.m. and EF improved to 55%. Figures 1 and 2 show typical electrocardiograms with and without ivabradine.An electrophysiological study (using the 3D Ensite system) was then proposed to the patient and in view of this, ivabradine was stopped for five half-lives. Figures 3 and 4 show this. The activation of this rhythm in the sinus node area was from caudal to cranial. This atrial tachycardia (AT) was mapped at the level of high right atrium below the appendage. The earliest activation was targeted and few seconds of radiofrequency application by a Blazer 4 mm tip catheter not irrigated (50 W, 508C) resulted in termination of AT ( Figure 5). The patient remained in normal sinus rhythm with no recurrence of arrhythmia for the 2 years of follow-up. The final diagnosis of this case was incessant automatic right-sided AT, originating from the anterior wall just below the appendage. Case 2A 24-year-old female presented to our outpatient clinic with incessant supraventricular tachyarrhythmia up to 160 b.p.m., also initially diagnosed as IST (Figure 6). She was offered an electrophysiological study but she refused. The patient was started on ivabradine 7.5 mg twice daily and metoprolol 50 mg twice daily, continued for .1 year and her HR was lowered to 70 b.p.m.Due to pregnancy, the patient stopped all medications, and after the seventh week of pregnancy she complained ofpalpitation,dyspnoea,andeasyfatigability.ThemeanHR was 140 b.p.m. The echocardiogram showed a reduced LVEF of 35%, suggesting a tachycardia-induced cardiomyopathy. Metoprolol 50 mg twice daily was resumed, but did not control her tachyarr...