The most common moments where a bystander can save a life share one thing: they happen fast, and the window to act is narrow. In cardiac arrest, brain damage begins in as few as 10 minutes. In severe bleeding, minutes matter. Knowing even the basics of a few emergency responses can be the difference between someone surviving or not. Here’s what to do in the situations where your actions matter most.
Cardiac Arrest: When Someone Collapses
Cardiac arrest is the emergency where bystanders have the single greatest impact on survival. The heart stops beating, the person collapses, loses consciousness, and stops breathing. There’s usually no warning. Without CPR, blood stops flowing to the brain, and permanent damage can begin within 10 minutes.
Your first step is calling 911. Your second is starting chest compressions immediately. Place the heel of one hand on the center of the person’s chest, put your other hand on top, and push hard and fast. You’re aiming for a depth of at least 2 inches and a rate of 100 to 120 compressions per minute (roughly the tempo of “Stayin’ Alive” by the Bee Gees). Let the chest fully recoil between each push. Don’t stop until paramedics arrive or the person starts breathing.
If you’re untrained or uncomfortable with rescue breaths, hands-only CPR (compressions without mouth-to-mouth) is not just acceptable, it’s actually more effective when performed by untrained bystanders. A meta-analysis of randomized trials found that survival at hospital discharge was 11.5% with compression-only CPR compared to 9.4% with standard CPR that included rescue breaths. The reason is straightforward: bystanders are more willing to start compressions when they don’t have to do mouth-to-mouth, and pausing compressions to give breaths interrupts blood flow to the brain. The key exception is drowning, which is covered below.
Using an AED
If an automated external defibrillator is nearby, grab it. These devices are designed for untrained people to use. They give voice prompts, analyze the heart rhythm, and only deliver a shock if one is needed. You cannot accidentally harm someone with an AED.
The impact is dramatic. Survival from cardiac arrest is about 9% with bystander CPR alone, but jumps to 24% when a bystander applies an AED, and reaches 38% when the AED delivers a shock. Put simply, early defibrillation nearly doubles a victim’s odds of survival. AEDs are commonly found in airports, gyms, offices, schools, and shopping centers. If someone nearby can grab one while you do compressions, that’s the ideal scenario.
Heart Attack vs. Cardiac Arrest
These are not the same thing, and confusing them can cost time. A heart attack is a blood flow problem: a blocked artery starves part of the heart muscle. The person is usually conscious and may feel chest pain or pressure, shortness of breath, nausea, sweating, or dizziness. Symptoms can be mild, especially in women and older adults. A heart attack requires calling 911, but the person is typically awake and breathing.
Cardiac arrest is an electrical problem: the heart stops pumping entirely. The person collapses, goes unconscious, and stops breathing. This is when CPR and an AED are needed. A heart attack can trigger cardiac arrest, which is why any chest pain should be taken seriously. If someone complaining of chest pain suddenly collapses and stops breathing, switch to CPR immediately.
Choking: Clearing a Blocked Airway
When someone is choking and can’t cough, speak, or breathe, you need to act before they lose consciousness. For adults and children over one year old, use abdominal thrusts (the Heimlich maneuver). Stand behind the person, wrap your arms around their waist, place your fist just above the navel, grab it with your other hand, and thrust sharply inward and upward. Repeat until the object is dislodged or the person becomes unconscious.
Infants under one year should never receive abdominal thrusts. Instead, hold the baby face down along your forearm with the head lower than the body, and deliver five firm strikes between the shoulder blades with the heel of your hand. If that doesn’t work, turn the infant face up and give five chest thrusts using two fingers on the breastbone, pushing about half an inch to an inch and a half deep. Alternate between back blows and chest thrusts until the airway clears. If the person (adult, child, or infant) becomes unconscious, begin CPR.
Severe Bleeding
Heavy bleeding from an arm or leg can become life-threatening in minutes. Your first move is direct pressure: press firmly on the wound with a clean cloth, shirt, or whatever fabric is available. Don’t let up. Steady, firm pressure is often enough to slow or stop bleeding until help arrives.
If blood is soaking through the fabric and direct pressure isn’t controlling it, a tourniquet can save a limb and a life. Place it two to three inches above the wound, between the wound and the heart. Avoid placing it directly on top of the wound or over a joint like the elbow or knee. Tighten it until the bleeding stops. Commercial tourniquets are increasingly available in first aid kits, workplaces, and public spaces. A belt or strip of fabric can work in a true emergency, though purpose-built tourniquets are far more effective.
Note the time you applied the tourniquet so you can tell paramedics. Once it’s on, don’t remove it. That’s a job for the hospital.
Opioid Overdose
Opioid overdoses kill by suppressing breathing until the brain is starved of oxygen. The signs are distinct: the person is unconscious or unresponsive, breathing is extremely slow or stopped, their pupils are tiny, their skin may be pale or grayish, and their lips or fingertips may turn purple. They may be limp and unable to speak.
Naloxone (commonly sold as Narcan nasal spray) reverses the effects of opioids and is available without a prescription in most pharmacies. The nasal spray requires no assembly. Lay the person on their back, insert the nozzle into one nostril, and press the plunger. If they don’t respond within two to three minutes, give a second dose in the other nostril. Even after they respond, call 911, because the overdose can outlast the naloxone and breathing may stop again.
If you don’t have naloxone and the person stops breathing, start CPR. Keeping oxygenated blood moving to the brain buys time until paramedics arrive.
Severe Allergic Reaction
Anaphylaxis can close the airway and crash blood pressure within minutes. If someone is having a severe allergic reaction (swelling of the face or throat, difficulty breathing, hives, rapid heartbeat) and has an epinephrine auto-injector, help them use it or administer it yourself. The injection goes into the outer thigh and can be given through clothing. Pull the safety cap straight off, press the device firmly against the outer thigh until you hear a click, and hold it in place for at least 3 seconds. Don’t put your fingers over the needle end.
Call 911 even after the injection. Epinephrine buys time, but the reaction can return as the drug wears off. Have the person lie down with their legs elevated unless they’re having trouble breathing, in which case sitting upright is better.
Drowning
Drowning is different from other causes of cardiac arrest because the core problem is oxygen deprivation, not an electrical malfunction in the heart. This means rescue breaths matter more here than in a typical cardiac arrest. If you’re trained, begin with two rescue breaths before starting chest compressions, then continue in cycles of 30 compressions to 2 breaths. Research shows drowning victims are significantly more likely to survive when CPR includes rescue breaths compared to compressions alone.
If you’re untrained or unwilling to give rescue breaths, compression-only CPR is still far better than doing nothing. Never attempt in-water rescue breathing unless you’ve been specifically trained to do so and can do it without putting yourself at risk. Get the person out of the water first, then start resuscitation on solid ground.
Legal Protections for Bystanders
Every U.S. state has some form of Good Samaritan law that protects people who provide emergency care in good faith. These laws shield you from negligence claims as long as you’re acting voluntarily, not expecting payment, and providing care that a reasonable person would attempt in the same situation. If the person is unconscious, the law assumes implied consent, meaning you don’t need permission to start helping. If the person is conscious and able to respond, ask before you act.
Good Samaritan laws don’t protect against reckless or intentionally harmful behavior, but they do cover the honest mistakes that can happen when an untrained person tries to help in a crisis. The legal system strongly favors people who try to help over those who stand by and do nothing.