The normal value of Troponin I is <0.2µg/L. Troponin I is checked by drawing venous blood. Troponin I is found in the muscle of the heart, i.e. the cardiac muscle cells, and is normally present in low levels in the blood. When the heart muscle is damaged, the Troponin I present in the cardiac muscle cells is released and enters the blood, resulting in a significant increase in blood Troponin I levels. The more severe and larger the extent of myocardial cell injury, the higher the level in the blood. Therefore, the level of troponin I in the blood can reflect the extent of myocardial cell injury. The measurement of troponin I is valuable for diagnosing myocardial injury diseases, such as acute myocardial infarction and myocarditis. Usually in patients with acute myocardial infarction, troponin I starts to rise 3-6 hours after the onset of the disease, and the rise reaches its highest value in 14-20 hours, and returns to normal in 5-7 days. If troponin I is found to be elevated in a patient with angina pectoris, it suggests a relatively small area of myocardial necrosis. A mild increase in troponin I may also be found in patients with acute myocarditis.