Background and Objective: Increasing exposure to magnetic and electromagnetic fields is inevitable. This study evaluates effect of MRI on ECG parameters of patients. Methods: This is an analytic study conducted in 2015 in the Gonabad MRI center. Eighty-four patients referred to the MRI center were recruited by convenient sampling. Two-lead ECG was measured before and after MRI. MRI was done by Neusoft machine, made in China, with 0.35 Tesla magnetic fields. Data analysis was done by SPSS, version 14.5, using pairwise t-test and Wilcoxon test (p<0.05). Results: Heart rate was 80.63 ± 10.41 beat/minutes before MRI and 71.58 ± 10.22 beat/minutes after MRI. QT interval was 9.70 ± 1.60 mm/s before MRI and 10.95 ± 0.93 mm/s before MRI (p<0.001). P-wave duration was 2.16 ± 0.47 mm/s before MRI and 2.12 ± 0.38 mm/s after MRI (p=0.45). QRS wave duration was 1.88 ± 0.51 mm/s before MRI and 1.88 ± 0.51 mm/s after MRI (p=0.64). PR interval was 4.33 ± 0.92 mm/s before MRI and 4.33 ± 0.78 mm/s after MRI (p=0.89). Discussion: Findings showed that 0.35-tesla MRI can increase QT interval and reduce heart rate; however, it is ineffective on P-wave duration, QRS and PR interval. To control the limitation, patients referred to MRI center for the second time were selected for the study. Moreover, the patients were kept under similar conditions before MRI to avoid moderate and severe anxiety. Conclusion: This study showed that 0.35 tesla MRI can reduce heart rate and increase QT interval. However, it is ineffective on P-wave duration, QRS and PR interval. Thus, it is suggested to measure these parameters before and after MRI.