Many clinical studies have evaluated the inflammatory response (mainly interleukin [IL]-6 and C-reactive protein [CRP]) after percutaneous coronary intervention (PCI) in patients with coronary artery disease (CAD). The aim of this study was to verify the source of possible elevation of IL-6 and CRP after PCI using coronary sinus sampling. We studied 87 subjects who underwent coronary angiography for diagnostic, therapeutic, or follow-up purposes. Blood samples were taken by the PCI team during the catheterization study from the coronary sinus. We measured coronary IL-6 levels by sandwich enzyme-linked immunosorbent assay, and high-sensitivity CRP levels were measured by latex immunonephelometry. The subjects were then classified according to their coronary angiographic findings into non-CAD (no evidence of significant organic CAD), mild CAD (1 vessel narrowed), and severe CAD (≥2 vessels narrowed) groups. PCI (including stent deployment) was performed in 16 patients with CAD. The mean coronary IL-6 value was higher in the severe than in the mild CAD group (3.67 ± 2.48 vs 2.3±1.15 pg/ml, p = 0.027). The mean coronary IL-6 value was higher in the subjects who underwent PCI than in those who did not (2.9 ± 1.23 vs 1.87 ± 0.9 pg/ml, p = 0.037), and the same was found regarding CRP (1.244 ± 0.72 vs 0.498 ± 0.51 mg/L, p = 0.032). The coronary IL-6 values correlated positively with the coronary CRP values (r = 0.374, p = 0.017). In conclusion, the increase in coronary IL-6 and CRP levels after PCI in patients with CAD might be attributed to their release from the coronary atheroma secondary to the direct mechanical effect applied on the atheroma itself by balloon inflation and stent deployment.