Ear-voice span (EVS) being vulnerable to such variables as language combination (Lee, 2006), Speaker’s delivery rate (Lyda, 2007, Wei, 2002), speech propositional density (Gile, 2008), etc. during the process of simultaneous interpreting (51) has been envisaged as a reliable measure of interpretation quality since the early discoveries in interpretation research (Gerver, 1976; Barik, 1973). This study aims at measuring the EVS patterns adopted during 51 in Persian/English language pair and assessing their effects on the quality of interpretations. In an experimental procedure, we compared the EVS patterns of two groups of 10 advanced trainees, one group interpreting from Persian into English and the other from English into Persian. With the aid of Sound Forge, a comparative analysis was made on synchronized SL-TL wave files to detect different EVS patterns adopted by the subjects. The quality assessment of interpretations demonstrated that the asymmetrical word order between the two languages highly influenced the subjects' online EVS choices leading them to select longer patterns during Persian-English51and, subsequently, more faulty interpretations.