Pyrimidine nucleotides are signaling molecules, which activate G protein-coupled membrane receptors of the P2Y family. P2Y(2) and P2Y(4) receptors are part of the P2Y family, which is composed of 8 subtypes that have been cloned and functionally defined. We have previously found that uridine-5'-triphosphate (UTP) reduces infarct size and improves cardiac function following myocardial infarct (MI). The aim of the present study was to determine the role of P2Y(2) receptor in cardiac protection following MI using knockout (KO) mice, in vivo and wild type (WT) for controls. In both experimental groups used (WT and P2Y(2)(-/-) receptor KO mice) there were 3 subgroups: sham, MI, and MI+UTP. 24h post MI we performed echocardiography and measured infarct size using triphenyl tetrazolium chloride (TTC) staining on all mice. Fractional shortening (FS) was higher in WT UTP-treated mice than the MI group (44.7±4.08% vs. 33.5±2.7% respectively, p<0.001). However, the FS of P2Y(2)(-/-) receptor KO mice were not affected by UTP treatment (34.7±5.3% vs. 35.9±2.9%). Similar results were obtained with TTC and hematoxylin and eosin stainings. Moreover, troponin T measurements demonstrated reduced myocardial damage in WT mice pretreated with UTP vs. untreated mice (8.8±4.6 vs. 12±3.1 p<0.05). In contrast, P2Y(2)(-/-) receptor KO mice pretreated with UTP did not demonstrate reduced myocardial damage. These results indicate that the P2Y(2) receptor mediates UTP cardioprotection, in vivo.