Cardiovascular disease has been associated with 40% of deaths in high-income countries and 28% in lower-income countries. The relationship between periodontitis and acute myocardial infarction is well documented, but it has not been established whether the extent and severity of periodontitis influence the infarct size. This cross-sectional and analytic study was designed to investigate the association of chronic periodontitis extent and severity with acute myocardial infarct size as indicated by serum cardiac troponin I and myoglobin levels. Sociodemographic, periodontal, cardiologic, and hematologic variables were gathered in 112 consecutive patients with myocardial infarction. The extent (Arbes Index) and severity (Periodontal Inflammatory Severity Index) of the chronic periodontitis were significantly associated with troponin I levels after controlling for sociodemographic and clinical confounders (change in R² = .041, p < .02, and R² = .031, p = .04). However, only the extent index accounted for levels of myoglobin (change in R² = .030, p < .05), total leukocytes (change in R² = .041 p < .02), and neutrophils (change in R² = .059, p < .01). Mediated regression analysis showed that leukocytes and neutrophils may underlie these observed relationships of chronic periodontitis with troponin I and myoglobin. To our knowledge, this study contributes the first research data demonstrating that the extent and severity of periodontitis is positively associated with acute myocardial infarct size as measured by serum troponin I and myoglobin levels.