[en] In previous in vivo studies with mice, rats, cats and monkeys, we have demonstrated that [7-methyl-¹¹C]-(E)-8-(3,4,5-trimethoxy styryl)-1,3,7-trimethylxanthine ([¹¹C]TMSX) is a potential radioligand for mapping adenosine A_2A receptors of the brain by positron emission tomography (PET). In the present study, we studied the potential of [¹¹C]TMSX for myocardial imaging. Uptake of radioactivity by the heart was high and gradually decreased after an intravenous injection of [¹¹C]TMSX into mice. In metabolite analysis, 54% and 76% of the radioactivity in plasma and heart, respectively, were present as the unchanged form of [¹¹C]TMSX 60 min postinjection. The myocardial uptake was reduced by carrier-loading and by co-injection of an adenosine A_2A antagonist CSC, but not by co-injection of an adenosine A₁ antagonist DPCPX. Pretreatment with a high dose of a non-selective antagonist theophylline also reduced the myocardial uptake of [¹¹C]TMSX. These findings demonstrate the specific binding of [¹¹C]TMSX to adenosine A_2A receptors in the heart. Finally we successfully performed the myocardial imaging by PET with [¹¹C]TMSX in a normal volunteer. A graphical analysis by Logan plot supported the receptor-mediated uptake of [¹¹C]TMSX. Peripherally [¹¹C]TMSX was very stable in human: >90% of the radioactivity in plasma was detected as the unchanged form in a 60-min study. We concluded that [¹¹C]TMSX PET has the potential for myocardial imaging. (author)