Heart failure is a common disease in which the heart can’t pump enough blood to meet the demands of the body. Many people may have heard of heart failure that prevents the heart from contracting properly or pumping enough blood. The measure most commonly used to calculate how well the heart contracts is called ejection fraction (EF). EF describes how much of the total blood volume in the heart is pushed out with every beat. EF often decreases after an event such as a heart attack and patients may develop heart failure.

Almost half of all people with heart failure have normal EF, but their hearts don’t fill with blood easily. This is called heart failure with preserved ejection fraction, or HFpEF (pronounced “heff peff”). In someone with HFpEF, the heart may contract normally, or even better than normal, but fill so poorly that there is not enough blood to pump out to meet the demands of daily life.

The filling of the heart depends on how stiff the heart tissue is and how quickly the heart muscle can relax. Heart stiffness increases with age because connective tissue called collagen builds up. People who also have other conditions such as diabetes or kidney disease are more likely to have increased heart stiffness.

Several chemical changes inside the cells need to happen so the heart can relax. Calcium releases inside the heart muscle cells, which activates enzymes. The enzymes cause changes in the proteins that make the heart contract. For the heart to relax, these chemical changes must be reversed so the calcium can return to its storage compartment in the cells. Both of these actions are slower in people with HFpEF, which means the heart may not be completely relaxed when it starts to fill with blood again.

Medications and exercise can improve quality of life for people with reduced EF, but so far there is no effective treatment for HFpEF. Research presented at the Experimental Biology meeting suggests that antioxidants may improve relaxation in the heart. However, more studies are needed to know if this will help people live longer. Another recent study found that antioxidants may increase fluid congestion that makes it harder for the heart to pump efficiently. These studies show how certain therapies affect people differently and suggest that individualized treatment—based on each person’s health—may be the best medicine.

Michael Hultström, MD, PhD, is a critical care anesthesiologist and associate professor of physiology at Uppsala University in Sweden. His research group works with circulatory function and the development of acute and chronic kidney damage both in experimental models and in patients undergoing major surgery.