Could blood work show if you had a heart attack?

Yes and No: There are characteristic abnormalities in the cardiac enzymes (blood work) that occur at the time of a heart attack and persist for days afterward. So blood work drawn drawn within hours to days of the heart attack is helpful. After the initial week, blood work normalizes and having labs drawn later will not show if you had a heart attack. At that point an ekg or echocardiogram are more helpful.

Yes: There are a number of tests that can show heart muscle damage. The most sensitive one is a test called a troponin-i level. That is basically only found in the heart, and if it is elevated, it may indicate heart muscle damage. The question remains if it is a current heart attack, or if it happened before. That can only be determined if you get a series of tests in a row.