BLS stands for Basic Life Support, a level of emergency medical care focused on keeping someone alive until more advanced help arrives. It covers the core, immediate interventions that matter most in life-threatening situations: recognizing cardiac arrest, performing CPR, clearing a blocked airway, and using an automated external defibrillator (AED). BLS is both a set of skills anyone can learn and a formal certification held by healthcare workers, first responders, and millions of trained bystanders.
What BLS Actually Involves
Basic Life Support is built around a simple chain of actions. First, you recognize that someone is in cardiac arrest or a similar emergency. Then you activate the emergency response system (calling 911 in the U.S.). From there, the physical interventions begin: chest compressions, opening the airway, providing rescue breaths, and using an AED if one is available. These steps form what the American Heart Association calls the first links in the “Chain of Survival,” and they exist to buy time for the heart and brain until paramedics can deliver more advanced treatments.
The reason BLS matters so much is timing. When bystander CPR starts within one minute of a cardiac arrest, about 22.4% of patients survive to leave the hospital with good brain function. When CPR is delayed to 10 minutes or more, that number drops to roughly 8.8%. Every minute without blood flow to the brain causes damage, so the gap between a cardiac arrest and the first chest compression is often the difference between life and death.
How CPR Works in BLS
Chest compressions are the single most important part of BLS. When the heart stops pumping on its own, pressing hard and fast on the center of the chest manually pushes blood to the brain and vital organs. Current guidelines call for a compression rate of 100 to 120 per minute, roughly the tempo of the song “Stayin’ Alive.” Each compression should push the chest down at least 2 inches (5 cm) in adults, but not deeper than about 2.4 inches (6 cm), since excessively deep compressions can reduce survival.
Quality matters as much as speed. The chest needs to fully recoil between compressions so the heart can refill with blood. Pauses in compressions should be as brief as possible. When two or more rescuers are working together, they should swap the compression role every two minutes, because fatigue degrades compression quality quickly even when the rescuer doesn’t feel tired.
For adults, the standard ratio is 30 compressions followed by 2 rescue breaths. For children, studies show that combining compressions with breaths (at either a 30:2 or 15:2 ratio) produces better outcomes than compressions alone, because children’s cardiac arrests more often stem from breathing problems rather than heart rhythm issues.
Opening the Airway and Giving Breaths
Before delivering rescue breaths, the airway needs to be open. The standard technique is a head tilt with a chin lift: one hand tilts the forehead back while the other lifts the chin forward. This prevents the tongue from falling back and blocking the throat. If a head or neck injury is suspected, trained rescuers use a jaw thrust instead, which opens the airway without moving the spine.
Each rescue breath should deliver just enough air to make the chest visibly rise. Blowing too hard or too fast can force air into the stomach, which causes vomiting and makes the situation worse. For someone who isn’t breathing but still has a pulse, one breath every 6 seconds (10 breaths per minute) is the target.
Using an AED
An AED is a portable device that analyzes the heart’s rhythm and delivers an electric shock if the heart is in a rhythm that can be corrected. You’ll find them mounted on walls in airports, gyms, schools, shopping centers, and many workplaces. They’re designed so that someone with no medical training can use one.
The process is straightforward: turn the device on, attach the adhesive pads to the patient’s bare chest (the pads have diagrams showing placement), and let the machine analyze the heart rhythm. If a shock is needed, the AED will tell you to press a button. If no shock is advised, you continue CPR. The key point is that an AED works alongside chest compressions, not as a replacement. Compressions should continue right up until the AED is analyzing or delivering a shock, and resume immediately after.
Choking Relief
BLS also covers foreign body airway obstruction, the clinical term for choking. If an adult or child is choking and cannot talk, cough forcefully, or breathe, the protocol starts with five firm back blows between the shoulder blades, followed by five abdominal thrusts (the Heimlich maneuver). You alternate between the two until the object comes out or the person becomes unresponsive.
For infants under one year old, the technique is different because their bodies are too small for abdominal thrusts. You hold the infant face-down along your forearm with the head lower than the body, deliver five back blows with the heel of your hand, then flip the infant face-up and give five chest thrusts using two fingers on the breastbone. For pregnant individuals or anyone whose abdomen you can’t reach around, chest thrusts at the base of the breastbone replace abdominal thrusts.
If you’re alone and choking, you can perform the Heimlich maneuver on yourself by placing your fist just above your belly button, grasping it with your other hand, and thrusting inward and upward against a hard surface like the back of a chair.
Recognizing Cardiac Arrest
One of the trickiest parts of BLS is recognizing that someone actually needs it. An unconscious person might still be breathing normally, or they might be exhibiting agonal breathing, which looks like slow, irregular gasps. Agonal breathing is not effective breathing. It’s a sign of cardiac arrest, and CPR should begin immediately.
For bystanders without medical training, the recognition check is simple: is the person responsive, and are they breathing normally? If the answer to either is no, call 911 and start compressions. Healthcare professionals are trained to check for a pulse at the neck, but even for them, the guideline is to spend no more than 10 seconds checking. If you can’t definitively feel a pulse in that window, start compressions. It’s far better to give compressions to someone who doesn’t need them than to withhold them from someone who does.
BLS vs. Advanced Life Support
BLS uses no drugs, no IVs, and no advanced airway devices. It relies on hands, lungs, and an AED. Advanced Life Support (ALS) builds on top of BLS with interventions like intravenous medication, advanced airway tubes, cardiac monitoring, and rhythm-specific drug protocols. Paramedics and emergency physicians provide ALS; EMTs, nurses, lifeguards, and trained bystanders provide BLS.
The distinction also applies to ambulances. A BLS ambulance carries oxygen delivery systems, manual ventilation bags, an AED, blood pressure cuffs, a pulse oximeter, a blood sugar meter, tourniquets, wound care supplies, splints, and basic medications approved under local protocols. An ALS ambulance adds cardiac monitors, advanced airway equipment, a broader pharmacy, and IV supplies. In many emergency medical systems, a BLS crew responds first and an ALS unit is dispatched when the situation calls for it.
Who Gets BLS Certified
BLS certification is required for most healthcare professionals: nurses, doctors, dentists, paramedics, EMTs, physical therapists, medical and nursing students, and many others. It’s also common among teachers, coaches, lifeguards, flight attendants, and personal trainers. The American Heart Association’s BLS course results in a certification valid for two years, after which a renewal course is required.
You don’t need to work in healthcare to take a BLS course. The skills are designed to be usable by anyone, and community versions of the training are widely available. Given that roughly 70% of out-of-hospital cardiac arrests happen at home, the person most likely to need your BLS skills is someone you know.