ACLS Algorithm: Master Cardiac Arrest, Bradycardia, and Tachycardia Protocols

The ACLS algorithm is the backbone of advanced cardiac life support. It tells you exactly what to do—step by step—when a patient goes into cardiac arrest, develops a dangerous bradycardia, or presents with an unstable tachycardia. There's no room for guessing. You follow the algorithm, make rapid decisions based on the rhythm, and act. Every second counts, and the acls algorithm framework exists because structured responses save more lives than improvisation.

The American Heart Association updates ACLS algorithms periodically based on new evidence. The 2025 guidelines refined several key recommendations—including epinephrine timing, airway management priorities, and the role of point-of-care ultrasound during resuscitation. Whether you're a nurse, paramedic, physician, or respiratory therapist, knowing these algorithms cold is non-negotiable. Your certification depends on it. More importantly, your patients depend on it. The difference between a provider who knows the algorithms and one who doesn't can literally be the difference between life and death in a cardiac emergency.

This guide breaks down every major ACLS algorithm you'll encounter on the exam and in clinical practice. We'll cover cardiac arrest (VF/VT and PEA/asystole), bradycardia, tachycardia, and the post-cardiac arrest care pathway. You'll also find free practice questions to test yourself after each section. Don't just read the algorithms—practice applying them until the decision points feel automatic.

Ready to test your knowledge right now? Scroll down to the quiz tiles and jump into a practice set. Or keep reading for the full algorithm breakdown with clinical pearls that textbooks leave out. Either way, you'll walk away more confident in your ability to run a code.

Understanding the full set of ACLS algorithms starts with recognizing that each one follows a similar logic: assess the patient, identify the rhythm, intervene based on the rhythm, and reassess. The differences lie in which interventions you choose. Cardiac arrest algorithms branch based on whether the rhythm is shockable or not. Bradycardia and tachycardia algorithms branch based on hemodynamic stability.

The bradyarrhythmia ACLS algorithm kicks in when the heart rate drops below 50 beats per minute and the patient shows signs of poor perfusion—hypotension, altered mental status, chest pain, or signs of shock. Your first move is atropine 1 mg IV, repeated every 3-5 minutes to a maximum of 3 mg. If atropine fails, you escalate to transcutaneous pacing, a dopamine infusion (5-20 mcg/kg/min), or an epinephrine infusion (2-10 mcg/min).

What trips people up on the exam is forgetting that atropine won't work for certain types of bradycardia. Specifically, it's ineffective in second-degree type II and third-degree (complete) heart block. In those cases, you skip straight to pacing. The algorithm accounts for this—but only if you read it carefully. Many test-takers default to atropine for every bradycardia scenario and lose points because of it. Know when to skip it and go straight to pacing—that's what separates a passing score from a failing one. The exam tests whether you understand the exceptions, not just the default pathway.

The ACLS algorithm 2025 updates brought several important changes that you need to know for your certification exam. The AHA now emphasizes early epinephrine administration for non-shockable rhythms—ideally within the first two minutes of recognizing PEA or asystole. For shockable rhythms, epinephrine is given after the second shock. This timing distinction is tested heavily on ACLS exams.

The bradyarrhythmia ACLS algorithm also received clarification in the latest guidelines. Point-of-care ultrasound is now included as a tool for identifying reversible causes during cardiac arrest—particularly for detecting cardiac tamponade, pulmonary embolism, and hypovolemia. While it's not a mandatory step in the algorithm, knowing when and how to integrate POCUS during a code gives you an edge in both clinical practice and exam scenarios.

The ACLS bradycardia algorithm remains largely unchanged from previous years: assess stability, give atropine if appropriate, escalate to pacing or vasopressors if the patient doesn't respond. But the 2025 guidelines emphasize that you should prepare for transcutaneous pacing early—even while waiting to see if atropine works. Don't wait for atropine to fail before getting the pads on the patient. Parallel processing saves time, and time saves lives. Have the pacing pads ready to go while you're pushing atropine through the IV line. That's how experienced code leaders operate.

The ACLS tachycardia algorithm is where many providers get confused—because tachycardia comes in so many forms. The first branch point is stability. Is the patient hemodynamically unstable? If yes, synchronized cardioversion. Period. Don't waste time with medications when the patient is crashing. Unstable means hypotension, altered consciousness, chest pain, or acute heart failure.

For stable patients, the algorithm tachycardia ACLS pathway branches again based on QRS width. Narrow complex tachycardia (QRS < 0.12s) is usually supraventricular in origin. Adenosine 6 mg rapid IV push is your first-line treatment for regular narrow-complex tachycardia—it works by briefly blocking the AV node. If that doesn't convert the rhythm, repeat with 12 mg. For irregular narrow-complex tachycardia (think atrial fibrillation), rate control with diltiazem or a beta-blocker is the standard approach.

Wide complex tachycardia (QRS ≥ 0.12s) is more dangerous. If it's regular and monomorphic, it's likely ventricular tachycardia—treat with amiodarone 150 mg IV over 10 minutes. If it's polymorphic (like torsades de pointes), IV magnesium 1-2g is the go-to. Never give adenosine for wide-complex tachycardia unless you're certain it's SVT with aberrancy. Getting this distinction wrong on the exam—or in real life—has serious consequences. When in doubt, treat wide-complex tachycardia as VT. It's the safer assumption because the treatment for VT won't harm an SVT patient, but misidentifying VT as SVT can be fatal.

The AHA ACLS algorithms are designed as decision trees. Every node is a yes-or-no question: Is there a pulse? Is the rhythm shockable? Is the patient stable? Your job is to follow the branches quickly and accurately. The algorithms aren't meant to replace clinical judgment—but they give you a framework that prevents critical steps from being missed during the chaos of a real code. Think of them as checklists for emergencies. Pilots use checklists for a reason. So should you, absolutely every single time.

When studying the ACLS SVT algorithm, pay attention to vagal maneuvers. Before reaching for adenosine, try a modified Valsalva maneuver or carotid sinus massage (in appropriate patients). These non-pharmacological interventions can terminate reentrant SVT by stimulating the vagus nerve and slowing AV node conduction. They don't always work, but they're low-risk and can resolve the arrhythmia without medication. The ACLS algorithm 2025 guidelines continue to recommend vagal maneuvers as a first-line intervention for hemodynamically stable SVT.

One clinical pearl that's worth remembering: when adenosine converts SVT, watch the monitor closely during the brief pause. That's your window to see the underlying rhythm—atrial flutter waves or other atrial activity that was hidden by the fast rate. This diagnostic information helps guide long-term management even after the acute episode resolves. Record or screenshot that rhythm strip—cardiology will want to see it later.

The VT/VF ACLS algorithm is arguably the most critical pathway to master. Ventricular fibrillation and pulseless ventricular tachycardia are shockable rhythms—meaning defibrillation is the definitive treatment. The earlier you deliver a shock, the better the odds. Every minute without defibrillation reduces survival by approximately 7-10%. That's why AEDs in public places matter so much. Early defibrillation by bystanders before EMS arrival can double or triple survival rates in out-of-hospital cardiac arrest.

In the ACLS VF/VT algorithm, the sequence after the first shock is CPR for two minutes, rhythm check, then shock again if VF/VT persists. After the second shock, give epinephrine 1 mg IV/IO. After the third shock, give amiodarone 300 mg IV. This alternating pattern of shock-CPR-drug continues until you achieve ROSC or the team leader decides to stop resuscitation efforts.

What separates good ACLS providers from great ones is minimizing hands-off time. Every pause in CPR—whether for rhythm checks, intubation, or other procedures—reduces coronary perfusion pressure. The AHA recommends keeping pauses under 10 seconds. Practice your rhythm analysis speed during simulation. You should be able to identify VF, VT, PEA, and asystole within 5 seconds of looking at the monitor strip. Use rhythm recognition apps and flashcards to drill this skill until it's reflexive. Speed here directly translates to better patient outcomes.

The ACLS VFib algorithm and the VT algorithm overlap significantly—both are shockable rhythms treated with defibrillation, CPR, and antiarrhythmics. The key difference is that VFib is chaotic and disorganized, while pulseless VT shows a regular wide-complex pattern. Clinically, the treatment is identical. On the exam, you need to recognize both rhythms visually and know that the ACLS algorithm VFib pathway applies to both.

Refractory VF—VFib that persists despite multiple shocks and amiodarone—is one of the most challenging scenarios in ACLS. Double sequential defibrillation (using two defibrillators simultaneously) has gained attention in recent years, though it's not yet part of the standard AHA algorithm. Some EMS systems use it as a last resort. For your ACLS bradycardia algorithm exam, stick with the standard protocol unless a question specifically asks about emerging therapies.

One mistake providers make during VF/VT arrest is focusing too much on intubation. Advanced airway placement shouldn't interrupt CPR. If bag-valve-mask ventilation is adequate, there's no rush to intubate during the first few rounds. The AHA specifically states that an advanced airway can be placed at any point during the arrest—but CPR should never be paused for more than 10 seconds to do it. Prioritize compressions and defibrillation above everything else. The airway can wait. The compressions can't. If the BVM is delivering adequate tidal volumes, an advanced airway adds risk without immediate benefit in the first few CPR cycles.

VTach ACLS management depends entirely on whether the patient has a pulse. Pulseless VT is treated identically to VF—immediate defibrillation followed by CPR, epinephrine, and amiodarone. But VT with a pulse is a completely different situation. If the patient is unstable (hypotensive, altered, chest pain), synchronized cardioversion is the answer. If stable, you have time to try antiarrhythmics first—amiodarone or procainamide IV.

The bradycardia ACLS algorithm deserves extra attention because it's straightforward but easy to rush through on exams. The algorithm starts with identifying signs and symptoms of poor perfusion. A heart rate of 45 in an athletic 25-year-old who feels fine? That's not a bradycardia emergency—it's normal for them. But a heart rate of 48 in a 70-year-old with syncope and a systolic BP of 80? That's the patient who needs immediate intervention per the algorithm.

Context matters in every ACLS scenario. The algorithms give you the framework, but you still need to apply clinical judgment. A rate of 55 with stable vitals needs monitoring, not atropine. A rate of 40 with signs of shock needs pacing, not more waiting. Train yourself to assess the patient first and the monitor second—that's what separates algorithm followers from skilled clinicians. The algorithm is your starting point—not your ceiling.

The VTach ACLS algorithm for pulseless VT follows the same defibrillation pathway as VFib. Shock, CPR, epinephrine, shock, CPR, amiodarone—repeat. The critical distinction is recognizing VT on the monitor: wide QRS complexes at a rate above 150, regular rhythm, and no discernible P waves. Monomorphic VT has uniform QRS morphology; polymorphic VT (including torsades de pointes) has varying QRS shapes and often requires IV magnesium instead of amiodarone.

The tachycardia ACLS algorithm is best memorized as a series of decision points. First: stable or unstable? Unstable gets cardioversion. Second: narrow or wide QRS? Narrow is usually supraventricular. Third: regular or irregular? Regular narrow-complex gets vagal maneuvers then adenosine. Irregular narrow-complex (usually A-fib) gets rate control. Each branch leads to a specific intervention—learn the tree and you'll handle any tachycardia question on the exam.

Polymorphic VT deserves special mention. If the QT interval is prolonged, it's torsades de pointes—give magnesium 1-2g IV. If the QT is normal, treat it like monomorphic VT with amiodarone. This QT distinction is a favorite exam question. Always check the QT interval before choosing your drug. The wrong antiarrhythmic for torsades can actually worsen the arrhythmia and trigger cardiac arrest. When you see polymorphic VT on the monitor, measure that QT interval before reaching for any medication.

The ACLS VT/VF algorithm comes down to three pillars: early defibrillation, high-quality CPR, and timely drug administration. When you practice these algorithms, time yourself. Can you identify the rhythm, charge the defibrillator, and deliver a shock within 15 seconds of the rhythm check? Can you resume CPR within 5 seconds after the shock? These time benchmarks matter because every delay reduces the odds of a good outcome.

For the V tach algorithm ACLS, remember that electrical therapy always takes priority over pharmacological therapy in unstable patients. A patient in VT with a BP of 60/40 doesn't need amiodarone—they need immediate synchronized cardioversion at 100J. The drug comes after you've stabilized the rhythm and the patient. Think of it this way: electricity resets the heart, drugs keep it from going back into the bad rhythm. This principle applies across all ACLS tachycardia scenarios: electricity first for unstable patients, medications first for stable ones.

Studying ACLS algorithms isn't something you do once and forget. Plan to review the flowcharts at least monthly if you work in acute care. Run through mental scenarios during quiet shifts—"If my patient went into VF right now, what would I do first?" This kind of mental rehearsal keeps the algorithms fresh and your response times fast. When the real emergency happens, you won't need to think about the steps. They'll be automatic. And that automaticity—built through repetition and practice—is what makes the difference when adrenaline is pumping and the patient's life hangs on your next decision.