Heart Attack in the Backcountry: Recognizing & Treating Myocardial Infarction on the Trail

Cardiac events are among the leading causes of death in the backcountry, and they don't discriminate by fitness level. The typical victim isn't out of shape — they're often an experienced hiker in their 50s or 60s who has been active their whole life, carrying an undiagnosed blockage that picks the worst possible moment to make itself known. Miles from a hospital, hours from an ambulance, the people around that person become the medical team.

The AOS free Wilderness First Aid course covers cardiac emergencies in detail because time is the single most critical factor in a heart attack. Every minute that goes by, the less likely the chance of surviving. If you suspect someone is having a heart attack, and it looks and acts like a heart attack, it is a heart attack until a physician says otherwise.

What Actually Happens During a Heart Attack

A heart attack — medically called a myocardial infarction, or MI — occurs when blood flow to the heart muscle itself gets blocked. The heart has its own blood supply system: the coronary arteries, which wrap around the outside of the heart and deliver oxygen to the muscle that keeps it beating. When one of those arteries gets blocked, the heart muscle downstream of the blockage starts to die.

Think of it as putting a tourniquet on the blood supply to the heart. The signs and symptoms you see — the chest pain, the sweating, the shortness of breath — are all caused by the heart's muscle dying in real time.

The location of the blockage determines severity. A blockage in a small coronary artery affects a small portion of the heart. A blockage in a major artery higher up — sometimes called a "widowmaker" — can affect most of the heart's muscle, and survivability rates drop fast. There is no such thing as a minor heart attack. All heart attacks are bad.

What causes the blockage

Most commonly, the patient has coronary artery disease — a buildup of plaques that narrows and hardens the arteries over time. Someone going into heart surgery may hear they had an 80% occlusion, meaning 80% of the artery is blocked. When the remaining passage can't deliver enough blood to the myocardium, the muscle starts to die.

Less commonly, a clot forms somewhere else in the body, breaks free, travels through the vessels, enters a coronary artery, and gets lodged. Either way, the result is the same: blocked blood flow, dying muscle, a medical emergency.

Risk factors include family history of coronary artery disease, smoking, obesity, and diabetes.

Angina vs. Heart Attack: The Warning You Can't Ignore

Here's where it gets tricky. Angina is essentially a heart attack that the patient didn't happen to die from at that moment.

Angina occurs when coronary arteries are partially blocked. At rest, the heart doesn't demand much oxygenated blood, so a 50% blockage might not cause symptoms. But when the patient starts hiking uphill, the demand increases, the partially blocked artery can't keep up, and the heart muscle starts suffering. The result: chest pain, anxiety, pain radiating to the neck, jaw, shoulders, and back, nausea, and pale, cool, clammy skin. It looks just like a heart attack — because it is one.

The deceptive part: the patient sits down, rests for 10 to 20 minutes, and all the symptoms go away. The demand dropped, so the partial blood flow became sufficient again. The patient declares they're fine, calls it a weird episode, and tells everyone not to worry.

Do not accept this. Treat it exactly the way you would treat a heart attack with symptoms that persist. Just because they got lucky this time does not mean they will not have a massive heart attack next time. Use your OPQRST assessment framework to characterize the episode fully, even if symptoms have resolved.

Signs and Symptoms of a Heart Attack

A myocardial infarction can present as one or many of the following:

Crushing substernal chest pain — in the middle of the chest, described as an elephant sitting on them
Shortness of breath — difficulty getting a full breath of air
Nausea, vomiting, and sweating
Pale, cool, and clammy skin
Radiating pain — to the neck, left or right shoulder, jaw, or back
A feeling of impending doom — the patient may say they feel like they're dying. Take this seriously.

One important diagnostic note from the course: if you can reproduce the chest pain by pressing on the chest or having them breathe deeply, it's probably not cardiac — it's more likely soft tissue, a strain, or a fracture. Chest pain from a medical condition like an MI can't be reproduced mechanically.

Atypical presentations

For a long time, the medical community thought women presented MI differently than men. That has since been disproven — the symptoms are largely the same. However, there is one behavioral difference: male patients often deny the heart attack is happening, while female patients tend to accept it but say they have other things to take care of right now. Neither response should delay your treatment.

The populations that truly do present differently are the elderly and diabetic patients. These groups may experience what's called a "silent heart attack" — vague symptoms like weakness, fatigue, or shortness of breath without the classic crushing chest pain. A silent heart attack is not a mild heart attack. It means the nerve signals got lost somewhere between the heart and the brain. The damage is the same.

Field Treatment Protocol

You have three tools in the backcountry for a suspected MI:

1. Keep them calm

The calmer the patient, the slower their heart rate and blood pressure, and the less stress on the heart. A panicking patient with a partially blocked coronary artery is putting more demand on a heart that can't meet it. Your composure directly affects their outcome. Speak calmly, explain what you're doing, and project confidence even if you don't feel it.

2. Aspirin — chewed, not swallowed

If the patient is not allergic to aspirin, administer it. The dose is 325 milligrams — that's four 81-milligram low-dose aspirin tablets (sometimes called "baby aspirin," though babies cannot have aspirin). They must be chewed, not swallowed whole, because chewing gets the medication absorbed quickly.

Aspirin is an antiplatelet drug. It prevents platelets from sticking together and forming larger clots, allowing blood cells to slip past the blockage. This is the best treatment available in the field — and it's the same thing an ambulance crew would give.

Make sure your wilderness first aid kit contains chewable aspirin. It's not the end of the world if it's not chewable, but make sure to administer the correct 325mg total dose.

3. Nitroglycerin (if prescribed)

Some patients with known heart conditions carry a nitroglycerin prescription. This is their medication, not yours — you're helping them take it. Nitroglycerin is a potent vasodilator that expands the blood vessels feeding the heart. If there's a blockage narrowing a vessel and you expand the passageway, blood can get through.

Key details: nitroglycerin typically comes in 0.4-milligram pills in a small brown bottle with a white top. The dose is 0.4mg every 15 minutes, as long as symptoms persist, up to three doses maximum. Always read the label — ignore the packaging.

Critical caveat: nitroglycerin dilates blood vessels throughout the entire body, not just the heart, which can cause an unsafe drop in blood pressure. Before administering, check for a strong radial pulse. If their pulse is weak, do not give this medication.

Nitroglycerin is a temporary measure — it relieves stress on the heart but does not solve the problem. Evacuation is still critical.

Evacuation: Always

A heart attack is always an evacuation. There is no "wait and see" with an MI. The question isn't whether to evacuate — it's how.

Ideally, the patient walks out, because walking is the fastest way to get anyone out of the backcountry. But there's a tension: physical exertion stresses the heart. The more they exert, the more demand on the heart, the worse the MI becomes, creating a feedback loop. The alternative is waiting for a rescue team to come in, which puts no stress on the heart but takes much longer.

The right decision depends entirely on the situation: distance to the trailhead, terrain difficulty, the patient's current condition, and available help. What you can control is having the information ready when you contact emergency services — the patient's symptoms, timeline, medications given, vital sign trends, and your exact location.

Regardless of the decision: if it looks like a heart attack, treat it like a heart attack until a medical provider says otherwise. The consequences of undertreating a real MI are devastating. The consequences of overtreating a false alarm are zero.

Prevention and Awareness on the Trail

You can't prevent a heart attack in the field the way you can prevent hypothermia or heat illness. But you can be aware of the risk factors in your group: age over 50, family history of heart disease, known coronary artery disease, diabetes, smoking history, and obesity. A participant assessment before a backcountry trip — using SAMPLE history — can surface these risk factors before you're three days from a road.

Carry chewable aspirin. Know who in your group has heart-related prescriptions and where they keep them. And know the fastest evacuation route from every point on your itinerary.

Learn the complete cardiac emergency protocol. Heart attacks, angina, and field treatment are covered in the medical emergencies module of our free online Wilderness First Aid course — 16+ hours of video instruction with no cost and no signup gate. Optional paid certification available.