When heart and blood vessel fat from heart failure patients was treated with methylene blue, the amount of harmful reactive molecules (like hydrogen peroxide) it produced went down.

When fat tissue around the heart and blood vessels from heart failure patients was soaked in a small amount of methylene blue for a day, the levels of a specific enzyme (MAO-A) that makes harmful molecules went down.

The fat directly on the heart makes more harmful molecules than the fat around the big blood vessels, even without any treatment.

The blue dye methylene blue cut the amount of a harmful chemical (hydrogen peroxide) in heart and blood vessel fat by about half when tested in the lab.

When fat tissue around the heart and blood vessels was soaked in a blue dye called methylene blue for a day in the lab, it made less of a harmful enzyme and produced fewer damaging chemicals, which might help explain how the dye could protect cells.