The effects of MDMA and loud noise on mouse heart tissue were examined in a study using nearly identical methods to those in a previous study by the same authors (Gesi et al. 2002a). Mice in this study were either injected with saline or with 20 mg/kg MDMA every 2 hours, with mice receiving 3 injections overall. (The previous study employed 2 or 4 injections of 30 mg/kg MDMA). Saline and MDMA-treated mice were either exposed to no noise or to speakers producing white noise at 100 dB, a level said match noise levels at nightclubs. As was reported in the previous study, no obvious morphological changes were observed in any of the mouse hearts under light microscopy. However, assessment with an electron microscope found that the combined treatment of MDMA and loud noise produced ultrastructural changes at the mitochondrial level including disorderly arrangement of cristae and a less dense matrix. Only slight changes in heart tissue were seen after MDMA or loud noise alone. The authors conclude that noise and MDMA might act synergistically on cardiac and perhaps other tissue, and propose that further research be done in exploring the combined effects of noise and MDMA administration on tissue function. It should be noted that mice are liable to find exposure to loud noise a stressful experience whereas humans attending dance events are liable to find it pleasurable. Hence some of the effects attributed to the combination of noise and MDMA may instead be the result of stress and MDMA.