The effects of MDMA given alone or in conjunction with loud white noise on the mouse heart were investigated in mice given either saline, 2 injections of 30 mg/kg MDMA or 4 injections of 30 mg/kg MDMA i.p. every 2 h, and either were or were not exposed to 6 h of 100 dB white noise. Myocardial tissue was removed from mice killed immediately after treatment had ended. 8 [mu]M slices of tissue were fixed, stained and examined with light and transmission electron microscope. Light microscopy failed to find structural alterations in tissue drawn from mice in any of the conditions. Examination via electron microscope found that both noise and either regimen of MDMA, when given alone, produced non-significant alteration in right atria at the mitochondrial level, such as swelling of mitochondrial membrane and dilution of the matrix. Loud white noise in combination with MDMA produced significant alterations in mitochondrial structure, and the effects of MDMA in this combined treatment were dose-dependent (the higher dose produced a greater reduction in mitochondria). The same pattern was evident in tissue from the right ventricle, with noise alone and MDMA alone producing non-significant damage to mitochondrial structure, while a combination of noise and MDMA produced significant structural alteration, and with MDMA effects being dose-dependent. While these study findings suggest that the combination of noise and MDMA may increase likelihood of cardiac problems, exposing mice to white noise is probably not equivalent to noise exposure for humans attending dance events. Dance event attendees presumably enjoy the loud music, whereas mice exposed to loud white noise almost certainly find it a stressful experience. Furthermore, humans attending dance events have probably acclimated to loud noise, whereas mice were not familiar with the experience and did not actively seek it. This being the case, stress may have played a role in the cardiovascular actions produced by MDMA and loud noise in this study. In addition, music is rhythmic, and findings in mice given methamphetamine (Morton et al. 2001) suggest that different effects may be produced by rhythmic versus non-rhythmic noise.