Mice with severe invasive pneumococcal disease showed elevated levels of troponin, a marker for heart injury, in their blood. They also had abnormal EKGs. When the researchers examined the hearts of the mice, they found microscopic sites of injury (called microlesions) in the heart muscle. S. pneumoniae were found within these microlesions, indicating the bacteria were able to invade and multiply within the heart. Looking in more detail, the researchers identified dying heart muscle cells in the tissue surrounding microlesions.