Homocysteine (Hcy) augments KCl-induced vasoconstriction in PVAT-intact IMAs. Representative concentration–response curve to KCl and concentration–response relationship pooled form 7 independent experiments (7 patients) in PVAT+E+ (A) and PVAT+E− (B) IMAs that were subjected or not subjected to Hcy exposure. **P < 0.01, ****P < 0.0001 versus control. IMAs: internal mammary arteries; PVAT: perivascular adipose tissue; PVAT+E+ IMA: IMA with both PVAT and endothelium, PVAT+E− IMA: IMA with PVAT but without endothelium.