BACKGROUND Patients with paroxysmal supraventricular tachycardia frequently present to the Emergency Department. Where vagal manoeuvres fail, the two most commonly used drugs are adenosine and calcium channel antagonists. Both are known to be effective but both have a significant side-effect profile. OBJECTIVE To examine the relative effects of adenosine and calcium channel antagonists and, if possible, to determine which is most appropriate for the management of supraventricular tachycardia. METHODS Studies were identified from The Cochrane Central Register of Controlled Trials (CENTRAL) on The Cochrane Library, Issue 2, 2010, MEDLINE (1966 to May Week 1 2010) and EMBASE (1980 to 2010 week 19). The searches were originally run in June 2006 and updated and re-run in May 2010. Bibliographies of identified studies were also examined. No language restrictions were applied. METHODS Randomised trials comparing adenosine and a calcium channel antagonist in patients of any age with supraventricular tachycardia, where one of the defined outcomes was reported. Outcomes of interest were: reversion rate, mortality, time to reversion, rate of relapse, major and minor adverse events, length of hospital stay and patient satisfaction. METHODS Two authors independently checked the results of searches to identify relevant studies. Dichotomous outcomes were reported as Peto Odds ratios and continuous outcomes as weighted mean differences. RESULTS A total of ten trials were identified (two new trials were identified through the updated search in May 2010), all of which used verapamil as the calcium antagonist. In the pooled analysis there was no significant difference in reversion rate between the two drugs. Time to reversion was slower for verapamil than adenosine in all studies that reported this outcome, but the data were not suitable for combining. Relapse rates were higher for adenosine compared with verapamil (OR 0.25, 95% CI 0.07 to 0.99. P=0.05). Minor adverse events such as nausea, chest tightness, shortness of breath and headache were reported much more frequently in patients treated with adenosine with 10.8 % of patients reporting at least one of these events, compared with 0.6% of those treated with verapamil (OR 0.15, 95% CI 0.09 to 0.26, P<0.001). Hypotension was reported exclusively in the verapamil treatment group (4/214), and occurred in none of the patients treated with adenosine (OR 10.8, 95% CI 1.46 to 80.22, P=0.02). CONCLUSIONS Adenosine and verapamil are both effective treatments for supraventricular tachycardia in the majority of patients. There is a high incidence of minor but unpleasant side effects and a greater risk of relapse in patients treated with adenosine while some patients treated with verapamil may develop significant hypotension. Patients should be fully informed of these risks prior to treatment.