Understanding Myocarditis: How Inflammation Can Weaken the Heart

Most people don’t expect their heart to become the weak point.

Myocarditis often begins with something ordinary: a virus, a few days of feeling unwell, a sense that your body will simply recover and move on. But in some people, the immune response meant to protect them does something very different. It becomes triggered and turns inward. Inflammation takes hold in the heart muscle itself, and suddenly a routine illness becomes a serious cardiac condition that can change how the heart works (and how life feels) for months or longer.

What Is Myocarditis?
Myocarditis is inflammation of the heart muscle, also known as the myocardium. The myocardium is responsible for the heart’s ability to pump blood throughout the body. When it becomes inflamed, the heart may struggle to pump effectively or maintain a normal rhythm.

Some people recover fully. Others experience lingering symptoms, reduced heart function, or complications that require ongoing care. What makes myocarditis especially challenging is how unpredictable it can be, both in how it presents and in how recovery unfolds.

What Causes Myocarditis?
In many cases, myocarditis is triggered by a viral infection. It can also be associated with autoimmune conditions, certain medications, or other inflammatory triggers.

Regardless of the original cause, much of the injury to the heart muscle is often driven not just by the infection itself, but by the body’s immune response. When inflammation becomes excessive or continues longer than it should, it can begin to damage healthy heart tissue.

Who Does Myocarditis Affect?
Myocarditis can affect people of many ages and backgrounds. It is often seen in otherwise healthy adults, and in many datasets appears more frequently in younger and middle-aged men.

Symptoms can include:
• Chest pain or pressure
• Shortness of breath
• Fatigue
• Heart palpitations
• Reduced ability to exercise

Because these symptoms overlap with other conditions, myocarditis can sometimes be difficult to recognize in its early stages.

How Common Is Myocarditis?
Estimates vary depending on how cases are tracked and diagnosed, but analysis suggest myocarditis occurs in the range of approximately 10 to 15 cases per 100,000 people each year in high-income countries.

Across North America, that translates to tens of thousands of cases annually. Many experts also believe myocarditis is underdiagnosed, particularly in milder cases that never reach a hospital or are attributed to other causes.

How Is Myocarditis Treated Today?
Treatment depends on how severe the disease is and how the patient presents.

In milder cases, care may involve rest and careful monitoring. In more serious cases, patients may require hospitalization and treatment to:
• Support heart function
• Manage arrhythmias
• Treat symptoms of heart failure

Today’s standard approaches are often supportive – focused on helping the heart cope while the inflammation resolves.

For many patients, this is enough. But for others, inflammation can leave behind lasting changes in the heart’s structure and function.

Why Inflammation Matters
Inflammation is not just an initial protective response that accompanies myocarditis. In many cases, it is a central driver of the damage to heart muscle.
That’s why the research field is increasingly focused on a critical question:
If we can safely and effectively reduce harmful inflammation in the heart, can we also support better recovery of heart structure and function?

For patients, this matters because myocarditis is not only about getting through the acute illness. It’s about what happens after, and whether the heart truly returns to normal.

How Cardiol Is Studying Myocarditis
At Cardiol Therapeutics, our work is built around the idea that targeting inflammation directly may help change the course of serious inflammatory heart diseases.

This approach was studied in the Phase II ARCHER trial, which evaluated CardiolRx™ in patients with acute myocarditis. We reported findings from ARCHER showing CardiolRx™ reduces inflammation-driven structural damage in the heart supporting the potential for myocardial recovery and reverse remodeling in this patient population. The treatment was shown to be safe and well tolerated in the study.

Why Structural Recovery Matters
When myocarditis damages the heart muscle, it can change the heart’s size, shape, and ability to pump effectively. These structural changes can influence long-term outcomes.

That’s why clinical findings related to reverse remodelling (i.e., the heart reverting back toward a healthier state with normalised size and restored function) are so important. They speak to the possibility of true recovery, not just temporary symptom improvement.

Looking Ahead
Myocarditis remains a serious and often unpredictable disease. While today’s treatments save lives and help many patients recover, there is still a need for therapies that address the underlying inflammatory mechanisms that drive heart muscle injury.

As research continues, the goal is not only to help patients survive myocarditis but to help their hearts heal more completely.