When heart cells don't have enough iron, their energy production systems break down, causing mitochondria to malfunction and forcing the cells to rely more on sugar for energy, which happens before the heart starts failing.

Giving iron directly into the bloodstream of mice with heart cell hepcidin deficiency stops their hearts from failing, proving that the heart problems are caused by the heart cells not getting enough iron.

When mice don't have hepcidin in their heart cells or have a version of ferroportin that can't respond to hepcidin, their heart cells lose too much iron, causing the heart cells to become iron deficient.

When mice lose the ability to make hepcidin in their heart cells, their heart cells don't get enough iron, which causes their hearts to weaken and eventually fail, even though their overall body iron levels are normal.

Giving iron directly into the bloodstream might help heart failure patients who are low on iron (even if they don't have anemia) by fixing the iron deficiency in their heart cells.