Why is a Normal Ejection Fraction a Warning in HCM?

If you have Hypertrophic Cardiomyopathy (HCM), an ejection fraction (EF) of 50% to 55% is a warning sign, even though it is considered a perfectly healthy number for someone without the condition. In a typical heart, a normal EF is between 55% and 70%. However, an HCM heart is usually hypercontractile (overactive)—meaning it squeezes much harder than a normal heart, often pumping out 65% to 75% of its blood with each beat ^[1][2]. For someone with HCM, a drop from these high numbers down into the 50–55% range means the previously thickened heart muscle is losing its abnormal strength and is beginning to weaken.

The Shift to Systolic Dysfunction

Why does this drop in squeezing power happen? Over time, the thickened, overworked heart muscle in HCM can undergo structural changes. The healthy muscle fibers can become replaced by scar tissue, a process known as myocardial fibrosis ^[3][4]. As this scar tissue builds up, the heart wall may actually thin out and lose its ability to pump forcefully ^[5][6].

When an HCM patient’s ejection fraction drops below 50%, cardiologists refer to this as the “burned-out” or “end-stage” phase of the disease ^[7][5][8]. It is critical to know that “end-stage” does not mean terminal or the end of your life. Instead, it is a medical term meaning the hypertrophic (thickened) phase of the disease has ended, and your heart has shifted into a phase of systolic heart failure (a weakened squeeze). Because an EF of 50-55% is right on the edge of this threshold, doctors treat it as a major red flag that the heart is transitioning toward this new phase, which remains highly treatable.

Symptoms to Watch For

As your ejection fraction drops, you may notice new or worsening physical symptoms. Because your heart is not pumping as efficiently, you should alert your doctor if you experience:

• Increased fatigue or exhaustion during normal activities
• New or worsening shortness of breath, especially when lying down
• Swelling (fluid retention) in your legs, ankles, or abdomen

Why a Dropping EF Changes Your Care

A declining ejection fraction requires a complete shift in how your medical team manages your condition, changing focus from calming an overactive heart to supporting a weakened one ^[9][10][11].

• Medication Adjustments: Standard HCM medications—such as beta-blockers, calcium channel blockers, or newer targeted drugs like mavacamten (Camzyos)—are designed to relax the heart and reduce its powerful squeeze. If your heart is naturally losing its pumping power, these medications could drop your EF dangerously low. In fact, strict safety protocols require doctors to stop targeted myosin inhibitors if your EF drops below 50% ^[12][13].
• New Treatment Strategies: To support your heart’s new phase, your doctor will likely introduce medications used for standard heart failure, such as ACE inhibitors, ARBs, SGLT2 inhibitors, or diuretics to help manage fluid buildup. In some cases, specialized pacemakers (CRT) or implantable defibrillators (ICDs) may be discussed.
• Advanced Imaging: Your doctor will likely order a cardiac MRI, which is the best tool to look for scar tissue (late gadolinium enhancement) and accurately measure how much the structure of your heart muscle has changed ^[6][14].

Understanding your “baseline” ejection fraction—what is normal for your heart—is crucial. A drop to 55% requires close monitoring and proactive adjustments to protect your heart’s remaining function.