Background: This retrospective study aimed to investigate the diagnostic relation between the mean platelet volume (MPV) and supraventricular tachyarrhythmia (SVT) in patient with documented atrial tachyarrhythmia in the emergency department (ED). Methods: Two study groups were compared; a SVT group with arrive at the ED with documented SVT (n=122) and 100 healthy adult without any palpitation symptom, arrhythmic disease, and with normal physical examination results that were brought for checkups to the cardiology polyclinic were classified as control group. Blood samples were obtained from all patients for determining the hematologic counts and MPV during first hour in ED period. Results: In terms of the focus of the study, hemoglobin, neutrophil count, mean cell volume (MCV), red cell distribution width (RDW), platelet, white blood cell (WBC), and lymphocyte counts were similar in both group (p>0.05). MPV in the SVT group was significantly higher than in the control group (9.12±1.22 flvs 8.64±0.89 fl, p<0.001). Multivariate logistic regression analysis showed that just MPV was independent predictor of SVT in patients with palpitation in ED (odds ratio [OR] 8.497, 95% confidence interval (6.181 to 12.325), p=0.012).Conclusions: The present study described that MPV is helpful parameter for the diagnosis of SVT in emergency department, for the first time in the literature.