(1) Background: This cross-sectional investigation appreciated the role of serum C-reactive protein (CRP), several hematologic-cell markers, and salivary inflammation-related molecules [calprotectin (S100A8/A9), interleukin-1β (IL-1β), kallikrein] to predict periodontitis in patients with atherosclerotic cardiovascular disease (ACVD), arrhythmia, or both. The gene discussed is KLK4; the disease is Arrhythmia.