Which enzyme is most specific for injury to heart muscle?

• A. Troponin-I
• B. Myoglobin
• C. ALT
• D. Serum aldolase

Answer: (A)

Cardiac troponin I is the most specific marker of heart muscle injury. It is part of the contractile apparatus in cardiac cells and has a cardiac-specific isoform that is not present in meaningful amounts in skeletal muscle. When heart muscle is damaged, troponin I is released into the bloodstream and remains elevated for days, making it a highly reliable indicator of myocardial injury and infarction.

Myoglobin rises very early after injury but is not heart-specific, since it is found in skeletal muscle as well; this limits its usefulness for confirming cardiac origin. ALT is a liver enzyme and does not reflect heart muscle injury. Serum aldolase is a general muscle enzyme and likewise lacks heart specificity.