Objective: To investigate the proportional variation of macrophage and T-lymphocytes subpopulations in acute coronary syndrome (ACS) patients, its association with periodontitis (P), and to compare with control individuals. Subjects and methods: Three groups of subjects participated: one group consisted of 17 ACS patients with P (ACS + P), another group consisted of 22 no ACS + P patients, and a control group consisted of 23 participants with gingivitis (no ACS + G). Macrophage, CD4 +, and CD8 + T-lymphocytes and CD4 + /CD8 + ratio values in gingival tissue were determined histometrically. Results: Significant differences were found among three groups regarding the mean number of macrophage (no ACS + P > ACS + P > no ACS + G; p < 0.05) and CD8 + T-lymphocytes (no ACS + P > ACS + P > no ACS + G; p < 0.05). Significant variations were observed between the groups both CD4 + T-lymphocytes densities (ACS + P > no ACS + P and ACS + P > no ACS + G; p < 0.05) and CD4 + / CD8 + ratio (no ACS + P < no ACS + G and ACS + P < no ACS + G; p < 0.05). Conclusions: The increased number of CD8 + T-lymphocytes in both group ACS + P and group no ACS + P resulted in a reduction of the CD4 + /CD8 + ratio in gingival tissue when compared with no ACS + G group. Clinical relevance: The decrease of CD4 + /CD8 + ratio in gingival tissue reflects periodontitis and may be associated with severe adverse outcomes in people with ACS.