Synchronized Direct Current Cardioversion (SDC) is an established therapy for the termination of supraventricular tachycardia (SVT - either atrio-ventricular nodal reentry tachycardia (AVNRT) or atrio-ventricular reentrant tachycardia (AVRT)) with poor perfusion. The evidence is extremely limited with regard to the safety and effectiveness of this therapy. In Australia, half of the eight ambulance services include SDC within their clinical practice guidelines for the management of poorly perfused SVT; however the degree of variation in the application of SDC across these guidelines suggests a need to quantify the practice. This case provides a previously unreported example of the safety and effectiveness of prehospital SDC for SVT (with poor perfusion precipitated by a Valsalva Maneuver) by Victorian paramedics, and discusses the available literature regarding the effectiveness and safety of this practice.