Endothelial dysfuntion procedes development of atherosclerotic plaque. Preliminary studies in animal models demonstrated important role of adventitia and perivascular adipose tissue (PVAT) in development of atherosclerosis. The aim of the present study was to characterise the inflammatory infiltration of PVAT with particular focus on the role of T cells as drivers of vascular inflammation. Methods: 108 patients, who underwent CABG surgery were enrolled. PVAT specimens from left coronary artery LAD and internal mammary artery IMA and subcutaneous tissue S.C. were fragmented and suspension of cells were analysed with cytometer. Acetylcholine-dependent IMA vasorelaxation and superoxide 02´- production in IMA were measured.Results: In PVAT LAD CD45+ cells percentage is 8- and 5-fold increased comparing with S.C. and IMA. CD3+ cell number per mg of PVAT tissue in LAD is 3- and 2-fold higher comparing with S.C. and IMA with effector memory cells predominance. CD3+ infiltration of PVAT LAD and IMA were correlated (r=0,29). Correlations between impaired IMA relaxation and increased CD3+, CD8+ infiltration of IMA were observed. Increased 02´- production in PVAT IMA and increased CD45+ i CD8+ infiltration were correlated. Infiltration of IMA with CD8+ with activation markers: HLA-DR (r=-0,31), CCR5 (r=-0,23) and CD25 (r=-0,57) were particularly strongly correlated with impaired IMA relaxation, Conlusions: Increased lymphocytic infiltration of activated CD8+/25+ cells in PVAT is a independent prediction factor of impaired endothelial function apart from classical atherosclerosis risk factors. (R2=0,38; p<0,01).