The presence of temporary myocardial pacing leads is considered a safety contraindication for magnetic resonance imaging (MRI). The aim of this ex vivo tissue study was to measure the heating effects at the tip of the leads using proton magnetic resonance spectroscopy ((1)HMRS) thermometry. The tissue effects were verified by histological analyses. Pig hearts with implanted temporary pacemaker myocardial pacing leads were examined by whole-body MRI at 1.5 Tesla. The tests were performed either by a sequence with high specific absorption rate (SAR) or by standard clinical sequences with lower SAR. Temperature changes were detected via (1)HMRS thermometry, by monitoring the frequency difference between water protons and the reference signals of N-methyl protons of creatine/phosphocreatine (Cr/PCr) and trimethylamine (TMA). Histology was performed using several staining techniques. Standard low-SAR and high-SAR sequences did not cause significant temperature increases in the myocardial tissue surrounding the implanted leads. There were no histopathological signs of thermal damage around the tips of the leads in any of the hearts or in a control implanted heart not subjected to MRI. The present data suggest that temporary pacemaker myocardial pacing leads may be compatible with MR scanning at 1.5 Tesla. However, further in vivo studies and carefully monitored patient studies are needed before final safety recommendations can be made.