Cardiac troponin generally is a test that detects damage to the heart muscle. Troponin is a protein that occurs in the blood only when the heart muscle is damaged, as in a heart attack. Other reasons for elevated troponin exist, but a heart attack is the most familiar. The test does not measure the low amounts of troponin normally in blood. Troponin T is highly sensitive (hs-TnT) and has been used for advanced tests.