Myocardial Infarction (Heart Attack): Types, ECG & Treatment

A myocardial infarction — a heart attack — happens when blood flow to part of the heart muscle is blocked long enough to injure it. Here's how STEMI and NSTEMI differ, how they're diagnosed, and how they're treated.

What is a myocardial infarction?

A myocardial infarction (MI) is death of heart muscle caused by prolonged loss of blood supply, almost always from a blocked coronary artery. A cholesterol plaque ruptures, a clot forms on it, and the artery is occluded — starving the muscle it feeds of oxygen. The territory affected depends on which coronary artery is blocked.

STEMI vs NSTEMI

	STEMI	NSTEMI
Artery	Completely occluded	Partially occluded
ECG	ST-segment elevation in contiguous leads	ST depression or T-wave changes (no ST elevation)
Troponin	Raised	Raised
Urgency	Emergency reperfusion	Urgent, risk-stratified

Localise a STEMI by lead group in our STEMI ECG guide.

Symptoms

The classic presentation is crushing central chest pain, often radiating to the arm or jaw, with sweating, nausea, and breathlessness. But presentations can be atypical — especially in women, older adults, and people with diabetes, who may have only fatigue, indigestion, or shortness of breath.

How it's diagnosed

• ECG — the first test; identifies STEMI immediately and guides emergency care.
• Troponin — a blood marker of heart-muscle injury that rises within hours and confirms infarction.
• History and risk factors — clinch the picture.

Treatment

The priority is restoring blood flow — time is muscle.

• Primary PCI — emergency angioplasty and stenting, the preferred STEMI treatment, with a door-to-balloon goal of 90 minutes or less. See PCI.
• Thrombolysis — clot-busting drugs when timely PCI isn't available.
• Antiplatelets and anticoagulation — aspirin plus a P2Y12 inhibitor and heparin (see cath lab medications).
• Supportive therapy — oxygen if hypoxic, nitroglycerin, pain relief, and beta-blockers where appropriate.

Complications

• Arrhythmias, including ventricular tachycardia and fibrillation
• Heart failure and cardiogenic shock
• Mechanical complications — acute mitral regurgitation, ventricular septal rupture

Key takeaways

• An MI is heart-muscle death from a blocked coronary artery.
• STEMI = full occlusion with ST elevation; NSTEMI = partial, without ST elevation.
• ECG plus troponin makes the diagnosis.
• STEMI needs emergency reperfusion — primary PCI within 90 minutes.

Frequently asked questions

What is a myocardial infarction?

Death of heart muscle caused by prolonged loss of blood supply, almost always from a coronary artery blocked by a clot on a ruptured plaque — commonly called a heart attack.

What is the difference between STEMI and NSTEMI?

A STEMI is a completely occluded artery with ST-segment elevation on the ECG; an NSTEMI is a partial occlusion with ST depression or T-wave changes but no ST elevation. Both raise troponin.

What are the symptoms of a heart attack?

Crushing central chest pain that may radiate to the arm or jaw, with sweating, nausea, and breathlessness — though presentations can be atypical, especially in women, older adults, and people with diabetes.

How is a myocardial infarction diagnosed?

With an ECG (which identifies STEMI immediately) and a troponin blood test that confirms heart-muscle injury, together with the clinical history.

How is a STEMI treated?

With emergency reperfusion — primary PCI (angioplasty and stenting) within about 90 minutes, or thrombolysis if PCI isn't available — plus antiplatelets and anticoagulation.

What does 'time is muscle' mean?

The longer a coronary artery stays blocked, the more heart muscle dies, so rapid reperfusion in a heart attack directly limits the damage.