Camzyos (Mavacamten): A Cardiologist's Guide to the First Myosin Inhibitor for Obstructive HCM

What Is Camzyos (Mavacamten)?

Camzyos, the brand name for mavacamten, is the first-in-class cardiac myosin inhibitor, a once-daily pill approved by the FDA in 2022 for adults with symptomatic obstructive hypertrophic cardiomyopathy. It’s the first drug we’ve ever had that treats hypertrophic cardiomyopathy (HCM) at its molecular root. Earlier medicines only eased the downstream symptoms.

To understand why that matters, you need a quick picture of the disease. In HCM, the heart muscle grows abnormally thick. When the thickening sits in the wall just below the aortic valve, it narrows the path blood takes as it leaves the heart. We call that obstructive HCM, and it’s what drives the breathlessness, chest tightness, and lightheadedness so many of my HCM patients describe. For decades the only medicines we had were beta-blockers, the calcium channel blocker verapamil, and an older drug called disopyramide. They help, and none of them touch the underlying problem. Camzyos does.

How Does Camzyos Work?

Camzyos works by calming an overactive heart muscle, reducing the number of muscle-protein bridges that form with each beat so the heart squeezes less forcefully and the obstruction eases. In plain terms, the HCM heart contracts too hard and too stiffly. Mavacamten dials that excess contraction back toward normal.

Inside every heart muscle cell are two proteins, actin and myosin, that grab onto each other and pull to create a heartbeat. In HCM, too many of these grips form, so the muscle contracts excessively and then can’t relax properly between beats. Mavacamten binds to myosin and reduces how many of those grips form. The wall below the valve stops crowding the outflow path as aggressively, the pressure gradient drops, and blood leaves the heart more freely. That’s a different approach from a beta-blocker, which mainly slows the heart rate. Camzyos goes after the force of contraction directly.

Who Is Camzyos For?

Camzyos is for adults with symptomatic obstructive HCM, specifically NYHA class II or III, meaning your symptoms limit you during ordinary or light activity. It’s approved to improve functional capacity (how far and hard you can exert yourself) and to ease symptoms.

In my Encinitas practice, the patient I think about for Camzyos is someone with confirmed obstruction on an echocardiogram who still feels limited despite a beta-blocker or verapamil, or who can’t tolerate those drugs at the doses needed. It isn’t for non-obstructive HCM, and it isn’t a first reflex for someone with no symptoms. The decision always starts with two questions: are you genuinely symptomatic, and do we have clear obstruction to treat. If the answer to both is yes, Camzyos earns a place in the conversation.

How Well Does Camzyos Work?

Two large trials, EXPLORER-HCM and VALOR-HCM, showed meaningful and durable benefits, both in how patients feel and in how many avoid surgery. These are strong results for a single drug.

In EXPLORER-HCM, 251 patients with obstructive HCM were randomized to mavacamten or placebo. After 30 weeks, 37% of patients on mavacamten hit the trial’s combined goal of better exercise capacity plus symptom improvement, compared with 17% on placebo. The proportion of patients who improved by at least one NYHA class was 65% on the drug versus 31% on placebo, and the pressure gradient across the outflow tract dropped sharply.

VALOR-HCM asked a more pointed question. It enrolled 112 patients whose symptoms were severe enough that they’d been referred for septal reduction therapy, the umbrella term for surgery or alcohol ablation to physically remove thickened muscle. After 16 weeks, only 18% of patients on mavacamten still met criteria for or went ahead with that procedure, against 77% on placebo. The long-term follow-up at 128 weeks held up well, with sustained symptom gains and lasting reductions in the outflow gradient.

Camzyos at a Glance: The Two Landmark Trials

Why Is Camzyos Only Available Through the REMS Program?

Because Camzyos reduces the force of the heartbeat, it can push the heart’s pumping strength too low in some people, so the FDA requires it be dispensed only through a safety program called the CAMZYOS REMS. REMS stands for Risk Evaluation and Mitigation Strategy, and it exists for exactly the reason the drug works. A medicine that deliberately weakens contraction can, in a minority of patients, weaken it more than we want.

The number that matters is your ejection fraction, the percentage of blood the heart pumps out with each beat. A normal value sits around 55% or higher. In EXPLORER-HCM, about 5% of patients on mavacamten had their ejection fraction dip below 50% during the trial. Those dips were usually temporary and recovered after pausing the drug, but they’re the reason for the whole monitoring structure.

What the REMS means for you in practical terms is this. Camzyos can’t be filled at your corner pharmacy. You and your prescriber both enroll in the program, the prescription goes through a certified specialty pharmacy, and your refills are tied to keeping up with your echocardiograms. You can read the patient details and enroll at the official CAMZYOS REMS patient site, and the manufacturer’s patient information site walks through what to expect. I know the extra steps feel like a hassle. They’re the price of using a drug this targeted safely, and in my experience patients settle into the rhythm quickly.

What Does the Camzyos Monitoring Schedule Look Like?

You’ll get an echocardiogram before your first dose and then on a set schedule, frequently at the start and less often once you’re stable. The echo is how we watch your ejection fraction so we can act before a dip becomes a problem.

Echocardiogram Schedule on Camzyos

If your ejection fraction falls below 50% at any visit, or if you develop heart failure symptoms, we interrupt the drug. After a pause of about 4 weeks, if your ejection fraction recovers to 50% or higher, we can restart at a lower dose. We also hold off on dose increases, and sometimes pause the drug, during a serious infection or a bout of atrial fibrillation, because those situations can stress an already sensitive heart.

How Is Camzyos Dosed?

The usual starting dose is 5 mg once daily, taken with or without food, and we adjust it based on your ejection fraction and the pressure gradient across your outflow tract. Available doses are 2.5, 5, 10, and 15 mg, and 15 mg a day is the ceiling.

Dosing isn’t a fixed ladder you climb on autopilot. At each checkpoint I look at your echo first. If your ejection fraction is healthy and your gradient is still high, we may step the dose up. If the gradient has responded nicely, we hold. The drug has a long and variable half-life, anywhere from about 6 to 23 days, so it takes weeks for any dose change to fully settle in. That’s why patience matters and why we don’t chase the gradient with rapid adjustments. Certain patients start at the lowest 2.5 mg dose from the outset, which brings us to drug interactions.

What Side Effects and Drug Interactions Should You Watch For?

The main safety concern is a fall in your heart’s pumping strength, and the most important interactions involve drugs that change how your body clears mavacamten. Most people tolerate Camzyos well day to day. The serious risks are manageable precisely because we monitor for them.

Mavacamten is broken down mostly by a liver enzyme called CYP2C19. Two things follow from that. First, some people are naturally “poor metabolizers” of CYP2C19, an inherited trait that’s more common in people of East Asian ancestry (around 13%). They clear the drug much more slowly, so levels run higher and we dose more cautiously. Second, other medicines that block or boost this enzyme can swing your mavacamten levels in dangerous directions. Strong CYP2C19 blockers (such as the antifungal fluconazole and the antidepressants fluoxetine and fluvoxamine) are not allowed with Camzyos. Drugs that speed up its breakdown (such as the antibiotic rifampin, the seizure medicines carbamazepine and phenytoin, and the herbal supplement St. John’s wort) are also off-limits, because they can sap its benefit and risk a rebound when stopped.

Tell every one of your doctors and your pharmacist that you take Camzyos, and check with us before starting any new prescription, over-the-counter product, or supplement. Combining Camzyos with other drugs that weaken contraction, including high-dose beta-blockers, verapamil, diltiazem, or disopyramide, calls for extra care and closer echo monitoring. This is a drug where the medication list you bring to clinic genuinely matters.

Can You Take Camzyos During Pregnancy?

No. Camzyos can harm a developing baby, so it shouldn’t be used in pregnancy, and anyone who can become pregnant needs reliable contraception during treatment and for 4 months after the last dose. This is a firm rule, not a soft caution.

One added wrinkle is that mavacamten can make some hormonal birth control less reliable. Combined hormonal contraceptives that use a progestin other than norethindrone should be avoided. If you’re of reproductive age and considering Camzyos, this is a conversation to have with both your cardiologist and your gynecologist before you start, so your contraception plan is solid from day one.

How Does Camzyos Compare to Aficamten and Surgery?

Camzyos is one of three good options for drug-resistant obstructive HCM, alongside the newer pill aficamten and the long-established septal reduction procedures. The right choice depends on your anatomy, your other conditions, and how you feel about lifelong medication versus a procedure.

Aficamten (brand name Myqorzo) is the second cardiac myosin inhibitor, FDA-approved in late 2025. It works by the same broad mechanism with a couple of practical advantages: fewer drug interactions and an easier titration curve. For patients who can’t manage Camzyos’s interaction list, aficamten is an appealing alternative. Septal reduction therapy, either surgical myectomy or alcohol septal ablation, physically removes the thickened muscle and remains the right call for many patients, especially younger ones or those who need other heart surgery anyway. None of these options cures HCM. I walk through all of them with patients in clinic, and you can read more about the full treatment picture in my guide to hypertrophic cardiomyopathy. Untreated, severe obstruction can also drive complications like valve strain and heart failure over time, which is why treating it well matters.

Frequently Asked Questions About Camzyos

Why can’t I get Camzyos at my regular pharmacy?

Camzyos is restricted to the CAMZYOS REMS safety program because it can lower your heart’s pumping strength. It’s dispensed only through certified specialty pharmacies, and your refills are linked to staying current on your scheduled echocardiograms. You enroll in the program along with your prescriber.

How long does it take for Camzyos to work?

You may notice symptom improvement within the first several weeks, but the drug has a long half-life and takes time to reach full effect. We assess your response with echocardiograms at weeks 4, 8, and 12, and we often adjust the dose over those first few months before settling on your maintenance dose.

What happens if my ejection fraction drops?

If your ejection fraction falls below 50%, we pause Camzyos. Most dips are temporary. After about 4 weeks, if your pumping strength recovers to 50% or higher, we can usually restart at a lower dose. This is exactly what the monitoring schedule is designed to catch early.

Do I have to take Camzyos forever?

Camzyos treats obstructive HCM but doesn’t cure it, so the benefit lasts only while you take it. Most patients stay on it long-term. If it stops working, isn’t tolerated, or your ejection fraction won’t hold, we reassess and consider aficamten or a septal reduction procedure.

Can I keep taking my beta-blocker with Camzyos?

Often yes, but with care. Beta-blockers, verapamil, diltiazem, and disopyramide all reduce the heart’s contraction or rate, so combining them with Camzyos calls for closer monitoring. I review your full medication list and adjust as needed when starting the drug.

Is Camzyos the same as aficamten?

No, though they’re cousins. Both are cardiac myosin inhibitors that reduce excessive contraction in obstructive HCM. Aficamten (Myqorzo) is newer, has fewer drug interactions, and is easier to titrate, while Camzyos has the longer track record and the larger body of long-term data.

What should I do before starting Camzyos?

Get your baseline echocardiogram, enroll in the REMS program with your cardiologist, review every medication and supplement you take, and, if you can become pregnant, confirm a reliable contraception plan. Then set up your follow-up echo visits so refills stay on track.

References

1. CAMZYOS (Mavacamten) Prescribing Information. Bristol Myers Squibb. Updated April 17, 2025.

2. Olivotto, Iacopo, Artur Oreziak, Roberto Barriales-Villa, et al. “Mavacamten for Treatment of Symptomatic Obstructive Hypertrophic Cardiomyopathy (EXPLORER-HCM): A Randomised, Double-Blind, Placebo-Controlled, Phase 3 Trial.” Lancet 396, no. 10253 (2020): 759-769.

3. Desai, Milind Y., Anjali Owens, Jeffrey B. Geske, et al. “Mavacamten in Patients with Hypertrophic Cardiomyopathy Referred for Septal Reduction (VALOR-HCM).” Journal of the American College of Cardiology 80, no. 2 (2022): 95-108.

4. Desai, Milind Y., Kathy Wolski, Anjali Owens, et al. “Mavacamten in Patients with Hypertrophic Cardiomyopathy Referred for Septal Reduction: Week 128 Results from VALOR-HCM.” Circulation 151, no. 19 (2025): 1378-1390.

5. Ostrominski, John W., Rong Guo, Perry M. Elliott, and Carolyn Y. Ho. “Cardiac Myosin Inhibitors for Managing Obstructive Hypertrophic Cardiomyopathy: JACC: Heart Failure State-of-the-Art Review.” JACC: Heart Failure 11, no. 8 (2023): 951-966.

6. Braunwald, Eugene. “Hypertrophic Cardiomyopathy.” New England Journal of Medicine 392, no. 6 (2025): 553-565.

7. Ommen, Steve R., Carolyn Y. Ho, Imran M. Asif, et al. “2024 AHA/ACC/AMSSM/HRS/PACES/SCMR Guideline for the Management of Hypertrophic Cardiomyopathy.” Journal of the American College of Cardiology 83, no. 23 (2024): 2324-2405.

Published on damianrasch.com. The above information was composed by Dr. Damian Rasch, drawing on individual insight and bolstered by digital research and writing assistance. The information is for educational purposes only and does not constitute medical advice.