Aim. To compare pH, electrical conductivity, dynamic viscosity, and C-reactive protein (CRP) in oral fluid in patients with periodontitis, ischemic heart disease (IHD), and their combination, and to assess independent associations of each condition with these parameters.

Materials and methods. Cross-sectional study, 83 participants: control (n = 20), periodontitis (n = 20), IHD (n = 22), and periodontitis + IHD (n = 21). pH, dynamic viscosity (at a shear rate of 11.3 s^-1), conductivity, and CRP (ELISA) were measured in unstimulated oral fluid. Kruskal – Wallis and Mann – Whitney tests (Holm correction), Spearman correlation, and multiple linear regression adjusted for age, sex, BMI, smoking, and diabetes mellitus were applied.

Results. Between-group differences were significant for all four parameters (p < 0.001). Median pH was 7.07 in controls, 6.75 in periodontitis, 6.71 in IHD, and 6.59 in periodontitis + IHD; conductivity increased from 3286 to 6524 µS/cm, dynamic viscosity from 4.95 to 11.3 mPa·s, and CRP from 1.83 to 39.15 ng/mL. After covariate adjustment, both IHD and periodontitis retained independent associations with all parameters (all p < 0.001). In the periodontitis subgroup (n = 41), disease stage correlated significantly with CRP (ρ = 0.429; p = 0.005) and bleeding on probing (ρ = 0.472; p = 0.002).

Conclusions. Periodontitis and IHD were associated with unidirectional changes in oral fluid, most pronounced in their combination; the most consistent differences were observed for pH, conductivity, and CRP. The findings support regular dental monitoring of comorbid patients and further prospective studies accounting for pharmacological therapy.