OBJECTIVE: To determine the optimal adenosine dose effective in supraventricular tachycardia (SVT) and underlying conditions affecting the effective dose in children. STUDY DESIGN: Experimental study. PLACE AND DURATION OF STUDY: Department of Cardiology, The Children's Hospital and Institute of Child Health, Lahore, from July 2008 to June 2011. METHODOLOGY: All children presenting with SVT were administered adenosine in rapid boluses according to PALS guidelines using incremental doses of 100, 200 and 300 µg/kg. The response was recorded on 12 lead ECG. Preexcitation was documented and echocardiography performed on all children after attaining sinus rhythm. Mann Whitney test and Kruskal-Wallis test were used as a test of significance to determine any difference in effective adenosine dose between normal heart and various underlying conditions, taking p < 0.05 as significant. RESULTS: Eighty five patients were treated for 110 episodes of SVT with adenosine. M:F ratio was 2.2:1. Their age ranged from 6 days to 14 years with mean age of 27.9 months. Adenosine was effective in reverting 97 episodes of SVT to sinus rhythm (88.2%). A dose of upto 100 µg/kg was only effective in 36.4% episodes of SVT. Two hundred µg/kg was effective in 44.3% of those not responding to 100 µg/kg dose (n = 31/70, cumulative 64.5%). A dose of 300 µg/kg was effective in further 25 patients not responding to lower doses (n = 25/38, 65.8%; cumulative 88.2%). Mean effective dose of adenosine was 185.3 + 81.0 µg/kg with median effective dose of 200 µg/kg. Significantly higher dose of adenosine was required in children with underlying pre-excitation, n = 18/97 (220.8 + 67.6 µg/kg vs. 177.2 + 81.9 µg/kg, p = 0.039). CONCLUSION: Adenosine is an effective medicine in treating SVT in children. A higher dose of 200 µg/kg may be used as first bolus particularly in children with pre-excitation.