Background— The safety and clinical utility of MRI at 1.5 T in patients with cardiac implantable devices such as pacemakers (PM) and implantable cardioverter-defibrillators (ICD) have been reported. This study aims to evaluate the extent of artifacts on cardiac magnetic resonance (CMR) in patients with PM and ICD (PM/ICD). Methods and Results— A total of 71 CMR studies were performed with an established safety protocol in patients with prepectoral PM/ICD. The artifact area around the PM/ICD generator was measured in all short-axis (SA), horizontal (HLA), and vertical long-axis (VLA) SSFP cine planes. The location and extent of artifacts were also assessed in all SA (20 sectors per plane), HLA, and VLA (6 sectors per plane) late gadolinium-enhanced CMR (LGE-CMR) planes. The artifact area on cine CMR was significantly larger with ICD versus PM generators in each plane ( P <0.001, respectively). In patients with left-sided ICD or biventricular ICD systems, the percentages of sectors with any artifacts on LGE-CMR were 53.7%, 48.0%, and 49.2% in SA, HLA, and VLA planes, respectively. Patients with left-sided PM or right-sided PM/ICD had fewer artifacts. Anterior and apical regions were severely affected by artifact caused by left-sided PM/ICD generators. Conclusions— In contrast to patients with right-sided PM/ICD and left-sided PM, the anterior and apical left ventricle can be affected by susceptibility artifacts in patients with left-sided ICD. Artifact reduction methodologies will be necessary to improve the performance of CMR in patients with left sided ICD systems.