Introduction: Supraventricular tachycardia (SVT) is a condition commonly found in emergency settings. Adenosine is recommended as the first-line treatment for stable patients, however, it is rapidly metabolized. The ACLS guidelines recommend administration of 6-mg adenosine intravenously (IV) with an immediate 20-ml normal saline solution (NSS) IV (double syringe technique; DST). However, adenosine diluted with NSS up to 20 ml IV (single syringe technique; SST) was as well found effective for terminating the arrhythmia. Hypothesis: The SST is non-inferior to the DST for terminating stable SVT. Methods: A pilot, single-blind, randomized, controlled study was conducted from January to December 2020 at 4 hospitals in the northeastern region, Thailand. Thirty patients who presented with stable regular narrow complex tachycardia, diagnosed as stable SVT by cardiologists, were enrolled. They were randomized into the DST and SST groups, 15 patients each. We evaluated the termination of SVT (turned to normal sinus rhythm), the average successful doses, and the complication rate of each group. Analyses were based on the intention to treat principle. Results: The termination rate was 91.7% and 83.3% in the DST and the SST group, P =0.990. The success rate of 6-mg adenosine was 75% and 66.7% in the DST and the SST group, P =0.640. The total administration dose was 8.2±4.9 mg in the DST group, and 10.0±5.9 mg in the SST group, P =0.432. There was no difference in the complication rate between both groups. Conclusions: Adenosine diluted with NSS up to 20 ml administered IV was non-inferior to the conventional technique for terminating SVT. A further definitive study with larger sample size is required.