The solid line represents troponin I. Troponin T is indicated by the dashed line. The dot/dash alternating line indicates CK-MB levels. Myoglobin levels are indicated by the dotted line. Myoglobin is the fastest protein to return to normal in the blood. Troponin I increases dramatically and stays high for a long time. Troponin T increases dramatically, but not until Troponin I has already peaked. CK-MB increases modestly without a discernible peak. CK-MB is the first to increase after a heart attack but troponins are more specific to heart muscle.