Troponin: Troponin is a protein in the heart muscle. It is liberated into the bloodstream when heart muscles are damaged. Usually measured troponins are troponin I and troponin T. Troponin estimation is a highly sensitive test to detect damage to the heart muscle. Troponin levels in the blood increase significantly within 6 hours of the damage to heart muscle (usually a heart attack) and peaks at about 24 hours.