What are the different causes of a heart attack if the heart does not have any blocked arteries? My father had a minor heart attack and when they scanned his heart to check for blockages there were none to be found. The doctor's said normally they wouldn't expect someone with a heart like his to have a heart attack but haven't given any explanation as to why it may have happened.

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The Society of Cardiovascular Angiography and Interventions has an excellent summary of the types of heart attacks on their web site. As you can see, the first type, STEMI, is generally due to blockages, but the other types are due only to partial blockages or no blockage at all.

He probably suffered one of the types of events other than a STEMI heart attack.

STEMI Heart Attacks

An ST-segment elevation myocardial infarction (STEMI) is a serious form of heart attack in which a coronary artery is completely blocked and a large part of the heart muscle is unable to receive blood. “ST segment elevation” refers to a pattern that shows up on an electrocardiogram (EKG).

This type of heart attack requires immediate, emergency revascularization which restores blood flow through the artery. This revascularization is achieved either with drugs in the form of thrombolytics (clot busters), which are given intravenously, or mechanically with angioplasty – a treatment using thin, flexible tubes called catheters to open the closed artery.

These catheters are positioned at the beginning of the coronary arteries (the arteries of the heart), and contrast dye is injected through them to enable the interventional cardiologist to gather images of any blockage in the coronary arteries. Very thin wires (guidewires) are then advanced beyond the blockage and the clot is sucked out and/or a small balloon is opened to push the blockage out of the way. A stent– a metal, mesh tube – is often inserted at the same time to permanently prop the cleared artery open to allow blood to flow through.

NSTEMI Heart Attacks

A non-ST segment elevation myocardial infarction (NSTEMI) is a type of heart attack that does not show a change in the ST segment elevation on an electrocardiogram and that results in less damage to the patient’s heart. However, these patients will test positively for a protein called troponin in their blood that is released from the heart muscle when it is damaged. In NSTEMI heart attacks, it is likely that any coronary artery blockages are partial or temporary.

Treatment for an NSTEMI heart attack consists of medication and evaluation for whether a blockage is present that should be treated with medication only, cleared through angioplasty or treated with cardiac bypass graft surgery.

Coronary Artery Spasm

A coronary artery spasm is when the artery wall tightens and blood flow through the artery is restricted – potentially leading to chest pain, or blood flow is cut off all together – causing a heart attack. Coronary artery spasm comes and goes. Because there may not be a build-up of plaque or a blood clot in the artery, a coronary artery spasm may not be discovered by an imaging test called an angiogram that is typically performed to check arteries for blockages.

Treatment for a coronary artery spasm consists of medications such as nitrates and calcium channel blockers.

Demand Ischemia

Demand ischemia is another type of heart attack for which blockages in the arteries may not be present. It occurs when a patient’s heart needs more oxygen than is available in the body’s supply. It may occur in patients with infection, anemia, or tachyarrhythmias (abnormally fast heart rates). Blood tests will show the presence of enzymes that indicate damage to the heart muscle.

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    I'm almost amused by the downvote without explanation. I guess I forgot to include not drinking milk as a possible cause.
    – Carey Gregory
    May 2, 2016 at 0:38

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