The primary drug used to restart the heart during cardiac arrest is epinephrine, also known as adrenaline. It has been the cornerstone of resuscitation for decades and remains the first-line medication recommended by the American Heart Association. Other drugs play supporting roles depending on the type of cardiac arrest, but epinephrine is the one given in nearly every case.
How Epinephrine Restarts the Heart
Epinephrine doesn’t shock the heart back into rhythm the way a defibrillator does. Instead, it works by tightening blood vessels throughout the body, which raises blood pressure in the aorta, the large artery leaving the heart. This pressure increase pushes more blood into the coronary arteries, the small vessels that feed the heart muscle itself. Without adequate blood flow to the heart, chest compressions alone often can’t generate enough pressure to restore a heartbeat.
After more than a few minutes of cardiac arrest, the blood vessels lose their tone and essentially go slack. At that point, epinephrine or another vasoconstrictor becomes essential for restoring cardiac activity. By squeezing those vessels back to a functional state, the drug gives chest compressions and defibrillation a much better chance of actually working.
How Epinephrine Is Given
The standard dose is 1 milligram, repeated every 3 to 5 minutes for as long as resuscitation continues. It’s typically delivered through an IV line, but when IV access isn’t possible (which happens frequently in emergencies), rescuers can use an intraosseous line, a needle placed directly into the bone marrow of the shin or upper arm. Both routes are equally effective at improving survival.
Intramuscular injection is another backup option, and studies have shown it works similarly to IV delivery. You may have seen movie scenes where a needle is plunged directly into someone’s heart. That technique, intracardiac injection, is not part of modern resuscitation. Today’s protocols rely entirely on IV, intraosseous, or intramuscular routes.
Drugs for Shockable Rhythms
Not all cardiac arrests are the same. When the heart is in ventricular fibrillation (quivering chaotically instead of pumping), the primary treatment is electrical defibrillation. But if repeated shocks fail to restore a normal rhythm, two additional drugs come into play: amiodarone and lidocaine. Both help stabilize the heart’s electrical activity and make it more likely that the next shock will succeed.
Current American Heart Association guidelines recommend either amiodarone or lidocaine for shock-resistant ventricular fibrillation. Lidocaine was once considered a secondary option but has been upgraded to an equal alternative. These drugs are particularly useful when someone’s arrest was witnessed, because treatment can begin quickly enough for the medications to make a difference. They are always used alongside epinephrine, not as replacements for it.
Magnesium for a Specific Rhythm
Magnesium sulfate fills a narrow but important role. It’s not recommended for routine cardiac arrest, but it is highly effective for one particular rhythm called torsades de pointes, a type of abnormal heartbeat linked to a prolonged electrical cycle in the heart. For that specific condition, intravenous magnesium can eliminate the dangerous rhythm entirely. Outside of that scenario, giving magnesium during cardiac arrest doesn’t improve outcomes.
Drugs That Treat the Underlying Cause
Sometimes the heart stops because of a correctable chemical imbalance rather than a primary electrical problem. The most common example is hyperkalemia, dangerously high potassium levels in the blood. Excess potassium disrupts the heart’s electrical signals and can cause it to stop. In those cases, calcium chloride and sodium bicarbonate are given alongside epinephrine. Calcium directly counteracts potassium’s effect on the heart, while bicarbonate helps shift potassium back into cells. These aren’t general-purpose cardiac arrest drugs. They’re targeted treatments for a specific, reversible cause.
What About Atropine?
If you learned CPR or watched medical dramas before 2010, you might remember atropine as a cardiac arrest drug. It was once standard treatment for non-shockable rhythms like asystole (flatline) and pulseless electrical activity. The American Heart Association removed it from cardiac arrest guidelines in 2010 after evidence showed it didn’t improve survival. Studies conducted after the guideline change confirmed that removing atropine made no difference in patient outcomes. Atropine is still used in other heart-related situations, like treating a dangerously slow heart rate in a conscious patient, but it’s no longer part of cardiac arrest protocols.
Why Drugs Alone Aren’t Enough
It’s worth understanding that no drug by itself restarts a stopped heart. Epinephrine improves the conditions needed for the heart to restart, but it works as part of a system: chest compressions keep blood moving, defibrillation corrects chaotic rhythms, and epinephrine boosts blood pressure so those interventions can succeed. In cardiac arrest caused by a shockable rhythm, defibrillation is the single most important intervention. Epinephrine supports it. For non-shockable rhythms, epinephrine and high-quality chest compressions are the primary tools while the medical team identifies and treats whatever caused the arrest.
The timing of epinephrine matters as well. Current guidelines recommend giving it as soon as feasible, particularly after initial defibrillation attempts have failed. Delays in establishing IV access can slow drug delivery, which is one reason intraosseous access has become a standard backup. Every minute without adequate blood flow to the brain and heart reduces the chance of a meaningful recovery.