Supraventricular tachycardia (SVT) is a dysrhythmia characterized rapid heart rate, typically with rapid onset. SVT accounts for over 50,000 emergency department visits per year. Of patients with regular, narrow-complex SVT, the mainstay of therapy includes adenosine and diltiazem. Adenosine is recommend by American and European guidelines as first-line therapy, however adenosine carries unique side effects that are potentially distressing to patients, including: feeling of impending death or doom, flushing, anxiety, shortness of breath, and chest discomfort. Diltiazem does not carry this side effect profile, but has typically been reserved as second-line treatment due to side effects of low blood pressure associated with this class of medications. Diltiazem and adenosine have not been well studied head-to-head to compare safety and efficacy of their treatment for SVT. The purpose of this study is to evaluate safety and efficacy of adenosine and diltiazem for SVT in the ED (as completed through chart review of specific patient-level outcomes) and capture patient and clinician perspectives of medication satisfaction (through administration of questionnaires).