Over six million Americans live with heart failure. In most cases, the disease is caused by a blockage of blood to the heart from coronary artery disease or a heart attack, leading to what’s called “ischemic” heart failure. Treatment options for ischemic heart failure generally aim to slow the progression of the disease rather than heal the damaged heart.

Now, research with dogs has identified a gene therapy that appears to reverse the damage from ischemic heart failure and improve survival.

Researchers suspected that a heart protein called cBIN1 played a central role in heart function. The protein occurs at lower levels in people with heart failure, and the less cBIN1 they have, the worse their symptoms. So the researchers aimed to restore cBIN1 to failing hearts by a gene therapy that provides extra copies of the cBIN1 gene.

Without the gene therapy, almost all dogs that had heart failure died before the end of the study as the disease progressed. But every dog that received the gene therapy survived to the end of the study.

And when the researchers took a closer look, it was clear that the treated dogs’ heart function was actually improving. The fraction of blood the heart could pump with each beat—the central measure of heart function—increased from the time of treatment, when it would normally continue to decrease as heart failure progressed. Other measures of heart function, from microscopic cell structure to chemical markers of heart health, also suggested that treated dogs’ hearts were actively healing.

The therapy also showed promising results for the less common form of heart failure.

Heart failure research is one of the few areas where dogs are an irreplaceable research model. Research in cells in a dish, or in smaller animals like mice, can provide valuable insights about how cells and organs work. But before a therapy can be provided to patients, research with animals that are more like humans is necessary.

Dogs have similar heart anatomy to humans, and they experience heart failure in similar ways. The researchers’ results are a necessary step to move the gene therapy into clinical trials. If the therapy shows similar results in clinical trials, it could help heal hearts and save lives.