Synchronized cardioversion is highly effective in terminating SVT (including AVRT and AVNRT), and when the patient is stable, this is performed after adequate sedation or anesthesia.94 Most stable patients with SVT respond to pharmacological therapy, with conversion success rates of 80% to 98% for agents such as verapamil, diltiazem, or adenosine. In some resistant cases, a second drug bolus or higher dose of initial drug agent might prove effective.87,96 Nevertheless, in rare instances, drugs may fail to successfully restore sinus rhythm, and cardioversion will be necessary. Synchronized cardioversion is inappropriate if the SVT is terminating and reinitiating spontaneously. IIa B-R 1. Intravenous diltiazem or verapamil can be effective for acute treatment in patients with hemodynamically stable SVT.87,89,92,97 See Online Data and 3. Intravenous diltiazem and verapamil have been shown to terminate SVT in 64% to 98% of patients. These drugs should be used only in hemodynamically stable patients. A slow infusion of either drug up to 20 minutes may lessen the potential for hypotension.97 It is important to ensure that tachycardia is not due to VT or pre-excited AF because patients with these rhythms who are given diltiazem or verapamil may become hemodynamically unstable or may have accelerated ventricular rate, which may lead to ventricular fibrillation. These agents are especially useful in patients who cannot tolerate beta blockers or experience recurrence after conversion with adenosine. Diltiazem and verapamil are not appropriate for patients with suspected systolic heart failure. IIa C-LD 2. Intravenous beta blockers are reasonable for acute treatment in patients with hemodynamically stable SVT.96 See Online Data Supplement 2. Evidence for the effectiveness of beta blockers in terminating SVT is limited. 