MONA mnemonic for MI: the four letters and what current guidance changed

What each letter of MONA stands for

M is morphine, an opioid once given to relieve chest pain and anxiety and to reduce the heart's workload. O is oxygen, given to raise the oxygen reaching damaged heart muscle. N is nitrates, usually sublingual or IV nitroglycerin, which dilate veins and coronary vessels to lower the heart's oxygen demand. A is aspirin, chewed, to stop platelets from building the clot further.

The order spells a word, not a sequence of care. An evidence review of the four drugs (PMC5866121) describes MONA as a teaching aid for adjunct treatment in acute coronary syndrome, not a priority list. Some courses extend it with extra letters for drugs given later in the admission, sometimes called MONA BASH; this page sticks to the four-letter form because that is what exam stems use.

When nurses actually use it

MONA is useful as a checklist in the first minutes of suspected MI: has the client chewed aspirin, does the saturation justify oxygen, can the pressure tolerate nitroglycerin, and is pain still present. MSD Manuals describes chewed aspirin and oxygen for hypoxemia as part of early care, often started by emergency teams before arrival.

It does not replace the rest of the first-hour work, such as a 12-lead ECG, IV access, continuous cardiac monitoring and serial troponins. Used as a memory hook for the bedside drugs, it helps. Used as the whole plan, it leaves out the treatments that open the artery.

Where MONA misleads: what changed and why

Oxygen is the biggest change. The 2025 ACC/AHA acute coronary syndrome guideline recommends oxygen for confirmed hypoxemia, saturation below 90 percent, to bring it to at least 90 percent. The evidence review notes that the AVOID trial found more recurrent MI and arrhythmias with oxygen in clients who were not hypoxemic, and DETO2X-AMI found no one-year mortality benefit. Routine oxygen for a client saturating 97 percent is the outdated answer.

Morphine moved down too. MSD Manuals warns that morphine and fentanyl can blunt some P2Y12 antiplatelet drugs and may worsen outcomes, so opioids are used only when nitroglycerin is contraindicated or has not relieved the pain. Nitrates relieve symptoms but, per MSD Manuals, large trials found no outcome benefit, and they are withheld for a systolic pressure under 90 mm Hg or a drop of more than 30 mm Hg from baseline. Aspirin is the one letter the review credits with lower cardiovascular mortality, from the ISIS-2 trial.

Worked scenario: applying MONA in the right order

Hypothetical scenario, not a real exam item: a 62-year-old man has crushing chest pain for 20 minutes. Pressure is 84/56, heart rate 104, SpO2 96 percent on room air. Orders include aspirin, oxygen, sublingual nitroglycerin and IV morphine as needed. Which order does the nurse question?

The nitroglycerin, because a systolic pressure under 90 mm Hg makes it unsafe; dilating veins further could deepen the hypotension. Aspirin can be given now. Oxygen is also not indicated at 96 percent. Morphine is the order the nurse clarifies with the prescriber before giving, since pain relief is still needed but the pressure is already low. A student working MONA left to right would give nitrates without checking the pressure.

The related exam trap

Questions built on MONA rarely ask what the letters mean. They hand you a client and ask which letter does not apply. The answer that trips people is reaching for oxygen as the automatic first action in every chest pain stem. Check the saturation in the stem first; if it is 90 percent or higher, oxygen is not the priority drug.

The second trap is low pressure before nitroglycerin. A systolic pressure under 90 mm Hg, or one that has fallen more than 30 mm Hg from the client's baseline, turns the N into a hold even while pain continues. When every option is a MONA drug, aspirin is usually the safest first pick unless the stem names an allergy or active bleeding.

Sources and further reading

Morphine, Oxygen, Nitrates, and Mortality Reducing Pharmacological Treatment for ACS: An Evidence-based Review (PMC5866121). MONA definition as a teaching aid, AVOID and DETO2X-AMI oxygen findings, morphine and antiplatelet delay, nitrates without mortality benefit, aspirin mortality benefit from ISIS-2.

MSD Manual Professional Version: Overview of Acute Coronary Syndromes. Oxygen for saturation under 90 percent, chewed aspirin prehospital, opioids used judiciously after nitroglycerin because of P2Y12 interaction.

MSD Manual Professional Version: Medications for Acute Coronary Syndromes. Nitrates lack outcome benefit; withhold for systolic pressure under 90 mm Hg or a fall over 30 mm Hg; morphine cautions and P2Y12 interference.

Guideline Central: 2025 ACC/AHA Acute Coronary Syndromes Guideline Spotlight. 2025 recommendation to give oxygen for confirmed hypoxia with saturation below 90 percent.