How do bacteria in my mouth get into my heart?

Through the bloodstream, via inflamed gum tissue. The gum tissue surrounding teeth is highly vascularized, full of blood vessels. When that tissue is inflamed by periodontal disease, the bacterial population of the periodontal pocket (dominated by gram-negative anaerobes, particularly Porphyromonas gingivalis) enters the bloodstream through the disrupted epithelial barrier with routine regularity. Not occasionally, every time you chew, brush, or floss, if your gums are infected, bacteria are translocating into your bloodstream.

Once in the bloodstream, these bacteria trigger a systemic immune response. Porphyromonas gingivalis has specific virulence factors that allow it to evade immune clearance, persist in the circulation, and interact with arterial endothelium. The finding that confirms what the mechanism predicts: oral bacteria have been identified in coronary artery plaque samples in studies conducted at the University of Helsinki, with a statistically significant presence exceeding what would be expected by chance. The bacteria that live in your gum pockets are found in the plaque in your coronary arteries. That is no longer an inference. It is a documented finding. (Pussinen et al., European Journal of Oral Sciences, 2023)

Cardiologist's calibrated position, Solid (1) for the bacteremia pathway as a factual finding. Promising (2) for its causal contribution to atherosclerosis.

What to do: Understand that periodontal disease is not a local dental problem. The bacteria and the inflammation are systemic. Treating gum disease is a systemic health intervention.

For the full picture, read The Appointment You've Been Skipping Is Protecting Your Heart.