I had a heart attack last week. the ecg was clear. angiogram showed healthy arteries with no blockages. bloodtest=0.40 of troponin.what caused it?

Hard to say: Many things (including renal failure, pulmonary embolus, etc) can cause a mild elevation of troponin. If an ekg and a coronary angiogram were negative i doubt that the elevated troponin was caused by a heart attack.

Takosubo ?: Could have been broken heart syndrome or apical ballooning which is a stress reaction that mimics heart attack. Great news on normal coronary arteries.