Atrial and junctional tachyarrhythmias occur frequently during the perioperative period for congenital cardiac surgery and can be a cause of increased morbidity and mortality. These rhythm disturbances that may be well tolerated in a normal heart can cause significant hemodynamic instability in patients with congenital heart defects, particularly during the postcardiopulmonary bypass period. Management of these arrhythmias presents more of a challenge, since currently available antiarrhythmic drugs can be ineffective and poorly tolerated. In this study, we examined the possible effect of dexmedetomidine, a primarily sedative drug, on atrial and junctional tachyarrhythmias. Though some animal data have shown that it can prevent certain types of ventricular tachycardia, its therapeutic role during these types of arrhythmias has not been studied. This was a retrospective, nonrandomized, noncontrolled study. Fourteen patients admitted to the cardiac intensive care unit and who received dexmedetomidine for both, sedation/analgesia and for junctional ectopic tachycardia (JET), atrial ectopic tachycardia (AET), reentry type supraventricular tachycardia (Re-SVT), atrial flutter (AF) or junctional accelerated rhythm (JAR) were included. Dexmedetomidine was used as a primary drug or as a rescue if other antiarrhythmics had been used. Our primary end-points were (a) conversion to normal sinus rhythm (NSR) within 3 min for Re-SVT, and 2 h for all other arrhythmias or (b) heart rate (HR) reduction to improve hemodynamics; JET or =20%, AF < or =150 bpm and for JAR prevention of progression to JET. The mean age and weight were 2 +/- 3 mo and 4 +/- 1.5 kg, respectively. Most of the arrhythmias (79%) occurred during the postoperative period. Dexmedetomidine was used as a primary treatment in nine and as a rescue in five patients. Ten patients (71%) received an initial loading dose of 1.1 +/- 0.5 microg/kg. A continuous infusion, 0.9 +/- 0.3 microg x kg(-1) x h(-1) was administered in 12 patients. Thirteen patients' lungs were mechanically ventilated. Adverse effects were seen in four patients (28%). Three had hypotension that responded to fluid administration and one had a possible brief complete atrioventricular (AV) block. Nine of the 14 patients were transiently paced with atrial (seven) or AV sequential (two) pacing to improve AV synchrony. The primary outcome with rhythm and/or HR control was achieved in 13 patients (93%). JET rate decreased from 197 +/- 22 to 165 +/- 17 bpm within 67 +/- 75 min of dexmedetomidine administration. Five of these patients converted to NSR in 39 +/- 31 h and one remained in JAR. All four patients with Re-SVT had resolution of their tachyarrhythmia. Three converted to NSR and one to JAR. One patient with AET (220-270 bpm) responded well with decreasing HR to 120 bpm within 35 min and to NSR in 85 min. One patient with AF failed to respond. In two patients with JAR, neither progressed to JET and HR decreased from 158 +/- 11 to 129 +/- 1 bpm. This preliminary, observational report suggests that dexmedetomidine may have a potential therapeutic role in the acute phase of perioperative atrial and junctional tachyarrhythmias for either HR control or conversion to NSR.