ACLS stands for Advanced Cardiovascular Life Support. It is a set of clinical protocols and algorithms that healthcare professionals use to manage cardiac arrest, stroke, dangerous heart rhythms, and other life-threatening cardiovascular emergencies. ACLS is both a treatment framework and a certification course, most commonly administered through the American Heart Association.
What ACLS Covers
ACLS is designed for situations where a patient’s heart has stopped, is beating dangerously fast or slow, or is otherwise failing in a way that threatens their life. The protocols guide medical teams through a structured, step-by-step response to these emergencies. Rather than a single procedure, ACLS is a collection of algorithms, each tailored to a specific scenario: cardiac arrest, abnormally fast heart rhythms (tachycardia), abnormally slow heart rhythms (bradycardia), stroke, and post-resuscitation care.
Each algorithm is essentially a decision tree. It tells the team what to assess first, what interventions to try, and what to do if the patient doesn’t respond. This standardized approach means that an emergency team in one hospital follows the same playbook as a team across the country, reducing errors during high-pressure moments.
How ACLS Differs From BLS
You may have also come across the term BLS, or Basic Life Support. BLS covers fundamental techniques that even non-medical bystanders can learn: CPR, clearing a blocked airway, rescue breathing, and using an automated external defibrillator (AED). These are the first things done when someone collapses and stops breathing or loses a pulse.
ACLS builds on top of BLS with more advanced interventions that require medical training and equipment. These include placing advanced breathing tubes to secure the airway, establishing IV access to deliver medications directly into the bloodstream, administering cardiac drugs, and using electrical therapies like defibrillation, cardioversion, and external pacing. BLS is what keeps a patient alive until more help arrives. ACLS is what that help looks like.
Key Medications Used in ACLS
During a cardiac arrest, the ACLS algorithm calls for specific drugs at precise intervals. Epinephrine, which stimulates the heart and raises blood pressure, is the cornerstone: 1 mg given intravenously every 3 to 5 minutes throughout the resuscitation effort. If the heart is in a shockable but persistent abnormal rhythm, amiodarone may be given to stabilize the electrical activity, with a first dose of 300 mg followed by a second dose of 150 mg if needed. Lidocaine is an alternative if amiodarone isn’t available.
These medications aren’t given in isolation. They’re part of a tightly coordinated cycle of chest compressions, rhythm checks, electrical shocks (when appropriate), and reassessment. The algorithms dictate exactly when each drug is administered relative to these other interventions.
Identifying Reversible Causes
One of the most critical parts of ACLS is figuring out why the patient’s heart stopped in the first place. A heart that arrests due to blood loss needs a very different treatment than one that arrests due to a drug overdose. ACLS organizes the most common reversible causes into a memorable framework called the H’s and T’s, a list of 12 conditions that medical teams systematically consider during resuscitation.
The H’s include low blood volume (hypovolemia), lack of oxygen (hypoxia), too much acid in the blood (acidosis), low blood sugar, abnormal potassium levels (either too high or too low), and hypothermia. The T’s cover a collapsed lung under pressure (tension pneumothorax), fluid compressing the heart (cardiac tamponade), poisoning or drug overdose (toxins), a blood clot in the lungs, and a heart attack.
Each of these has specific signs that the team looks for, often on a heart monitor or through rapid bedside tests. Identifying and treating the underlying cause is frequently the difference between a successful resuscitation and one that fails, because CPR and medications alone won’t save someone whose heart stopped due to a problem that’s still present.
Post-Resuscitation Care
ACLS doesn’t end when the heart starts beating again. The return of a pulse is only the beginning of a critical phase called post-cardiac arrest care. Patients who are unresponsive to verbal commands after resuscitation now receive controlled temperature management for a minimum of 36 hours, according to the most recent 2025 American Heart Association guidelines. This involves carefully controlling body temperature to protect the brain from further damage during recovery.
The post-resuscitation algorithm also involves identifying what caused the arrest, stabilizing blood pressure and oxygen levels, and monitoring for dangerous heart rhythms that could trigger another arrest. Many patients are transferred to an intensive care unit for ongoing monitoring during this vulnerable period.
Who Needs ACLS Certification
ACLS certification is required for healthcare professionals who direct or participate in managing cardiac arrest and other cardiovascular emergencies. This includes physicians, nurses, and paramedics working in emergency departments, intensive care units, operating rooms, and emergency response teams. Many hospitals require ACLS certification as a condition of employment for clinical staff in these settings.
The certification is earned through a course that combines didactic learning with hands-on simulations of emergency scenarios. Upon completion, providers receive a card valid for two years, after which they must renew by taking an updated course. This renewal cycle ensures that providers stay current with guideline changes, which the American Heart Association updates periodically. The most recent major update came in 2025, which consolidated previous versions of the emergency response framework into a single unified chain of survival and updated recommendations for electrical therapies and temperature management.
What the 2025 Guidelines Changed
The 2025 American Heart Association guidelines introduced several notable updates to ACLS practice. The initial energy setting for electrical cardioversion of certain rapid heart rhythms (atrial fibrillation and atrial flutter) is now recommended to start at 200 joules or higher, up from lower previous settings. All patients with a specific type of dangerous rhythm called sustained polymorphic ventricular tachycardia now receive immediate defibrillation.
The guidelines also refined how providers think about abnormal heart rhythms during emergencies. A key emphasis is distinguishing between rhythms that are causing the patient’s instability and rhythms that are a symptom of some other underlying problem. That distinction changes the treatment approach entirely. The guidelines also strengthened recommendations for on-scene resuscitation during out-of-hospital cardiac arrest rather than rapid transport, reflecting evidence that high-quality CPR and early intervention at the scene improve outcomes.