Hypertrophic Cardiomyopathy (HCM)

It is the most common heart disease in cats, affecting up to 30% of cats aged 9 years and above. 

Obstructive HCM (HOCM)

Some cats also have HOCM, where the thickened muscle blocks blood flow out of the heart. This is the “obstructive” type.

Heart Failure in HCM or HOCM

As disease progresses, fluid can build up in the lungs (pulmonary edema) or chest (pleural effusion) or blood clots can form.

Some cats show signs like:

• Fast or difficult breathing

• Lethargy or hiding

• Sudden leg weakness (from clots)

 

Current Treatment

There’s no effective cure yet. Medications help manage symptoms, but they don’t stop the heart from thickening.

Common drugs used are:

• Diuretics remove excess fluid

• Beta-blockers may help slow the heart rate and reduce obstruction, though studies have not proven a clear benefit.

• ACE inhibitors may support circulation and reduce heart strain, but effectiveness remains unproven in cats.

• Blood thinners prevent clots.

 

Mavacamtem: What is it?

Mavacamten is a new drug developed for humans with the same disease. It is a myosin inhibitor which helps the heart relax and pump more efficiently.

• In a study evaluating human patients with HOCM, treatment with Mavacamten has been shown to improve exercise capacity, reduce LVOT obstruction, and enhance both NYHA functional class and overall health status.

What Research in Cats Shows?

One study using a drug like Mavacamten (called MYK-461) in cats with naturally occurring HCM found that it reduced how forcefully the heart contracted and improved blood flow obstruction.

However, the drug in that study was given as a single intravenous dose, and its long-term safety and dosing for everyday use remain unknown.

Current research in cats is still very limited, but these early findings give hope that future treatments could directly address the disease process.

It is worth mentioning that the exact safe dose and duration for cats are not yet established.

At this stage, using Mavacamten or similar drugs in cats is experimental.

Its use must always be advised, prescribed, and closely monitored by a veterinary cardiologist, with regular heart scans and examinations to ensure safety and effectiveness.

 

My Clinical Experience

Thankfully, Mavacamten has become available in Malaysia in July 2025, although it remains exceedingly expensive.

As Felycin-CA1 (Rapamycin) is not currently accessible, two cats with end-stage HCM were treated with Mavacamten for 14 days, under owner consent.

Preliminary results:

✅ Both cats showed reduced wall thickness.

✅ Their owners observed that the cats became more active clinically.

⚠️ However, one cat developed mild pleural effusion, requiring an increased diuretic dosage. The dosage of Mavacamten was reduced in both cats. 

 

In Short

HCM and HOCM can be serious, but with early diagnosis and proper care, many cats can still enjoy long and happy lives. 

Not all cats require treatment. 

Mavacamten may open a brighter chapter in this frustrating feline heart disease in Malaysia with limited accessible drugs. However, it’s not indicated in all cats. Further studies are still needed to confirm its long-term safety and benefits.

Stay tuned for more updates!