Cardiovascular diseases, including atherosclerosis and myocardial ischemia, occur as a result of a complex set of genetic and environmental factors. During periodontitis, dental plaque microorganisms may disseminate through the blood to infect the vascular endothelium and contribute to the occurrence of atherosclerosis and risk of myocardial ischemia and infarction. Myocardial ischemia and infarction are often preceded by acute thromboembolic events. In an in vitro model of thrombosis, certain dental plaque bacteria induce platelets to aggregate. Aggregation of platelets is induced by the platelet aggregation-associated protein [PAAPJ expressed on plaque bacteria, including Streptococcus sanguis and Porphyromonas gingivalis. Intravenous infusion of S. sanguis into rabbits has been shown previously to cause changes in the electrocardiogram (ECG), heart rate, blood pressure, and cardiac contractility. These changes are consistent with the occurrence of myocardial infarction. The ECG changes are now shown to begin within 30 seconds after infusion of PAAP+ S. sanguis, followed by alterations in blood pressure and respiratory rate. These changes occurred intermittently over a 30-minute period and changed within one heartbeat to a normal pattern and suddenly back to abnormal. Intermittent ECG abnormalities were seen in 13 of 15 rabbits, including left axis deviation, ST-segment depression, preventricular contractions, alternans, and bigemnia. Dose-dependent thrombocytopenia, accumulation of 111Indium-labeled platelets in the lungs, and tachypnea also occurred. No changes occurred with the PAAp- strain. The data indicated that PAPP+ S. sanguis interacts with circulating platelets, inducing thromboemboli to cause the pulmonary and cardiac abnormalities. During periodontitis, therefore, PAAP+ S. sanguis and P. gingivalis bacteremia may contribute to the chance of acute thromboembolic events.