Introduction: Paroxysmal supraventricular tachycardia (PSVT) is a common group of arrhythmias that Advanced Care Paramedics (ACPs) can often manage with vagal maneuvers, adenosine, and/or cardioversion, provided that they correctly identify the rhythm. The purpose of this study is to determine the accuracy of ACP identification of PSVT. Methods: Following ethics approval, all calls for patients 18 years with a 12-lead ECG available, who were assessed by ACPs within a region of western Ontario between July 2015 - December 2015 and had a documented heart rate>150bpm, were included. Paramedic call reports were retrospectively reviewed for study data, including documentation of ACP identified PSVT. The reference standard was consensus between an EMS fellow and prehospital physician who adjudicated each ECG for the presence of PSVT in a blinded, independent fashion. In the event of a disagreement, a third, blinded prehospital physician was used for consensus. Results: Of the 442 patients included, 197 (45%) were male and the median age [Interquartile range(IQR)] was 70.0 (58.0-82.8). ACPs identified 74 (16.7%) patients as having PSVT while 38 (8.6%) were identified by physicians as having PSVT. 44.7% of patients with physician identified PSVT had a history of previous arrhythmia, compared to 30.9% of patients with no physician identified PSVT (p=0.10). They were also significantly younger 58.5 (48.5-72.0) compared to those without physician identified PSVT 69.0 (60.0-84.0) (P=0.0010). Sensitivity of ACP identified PSVT was 97.4% (95%CI:86.2%-99.9%) and specificity was 90.8% (95%CI:87.6%-93.5%). The positive predictive value (PV) of ACP identified PSVT was 50.0% (95%CI:42.3%-57.7%), the negative PV was 99.7% (95%CI:98.1%-99.9%), the positive likelihood ratio (LR) was 10.6 (95%CI:7.8-14.5) and negative LR was 0.03 (95%CI:0.0-0.2). Moderate inter-rater agreement was seen between initial ECG interpretations (kappa= 0.42, 95%CI:0.29-0.54) by the fellow and prehospital physician, while agreement was higher (good) between the two prehospital physicians (kappa=0.76, 95%CI:0.55-0.96). Conclusion: These results indicate that ACPs are adept at identifying PSVT, but are prone to false positives. Given the relatively good sensitivity and specificity seen in this investigation, future studies should investigate ACP recognition of specific rare arrhythmias (antidromic accelerated atrial fibrillation) that may require different management including avoidance of adenosine.