For the study, researchers analyzed MRI scans performed on nearly 3,000 older adults, ages 54 to 94, without preexisting heart disease. Participants were followed between 2002 and 2012, at six hospitals across the United States where each one of them underwent MRI testing at the beginning of the study and once more after a decade.
The MRI scans provided researchers with 3-D images of the heart's interior and exterior, allowing them to determine the size and volume of the heart muscle. Adding these to the already known density of the muscle, they were able to calculate its weight.
Over a period of 10 years, the weight of the heart's main pumping chamber -- the left ventricle -- increased by an average of 8 grams in men and decreased by 1.6 grams in women. The heart's filling capacity -- marked by the amount of blood the left ventricle can holds between heartbeats -- declined in both sexes but more precipitously so in women, by about 13 milliliters, compared with just under 10 milliliters in men.
In men, the study reveals, the heart muscle that encircles the chamber grows bigger and thicker with age, while in women, it get retains its size or gets somewhat smaller.
"Thicker heart muscle and smaller heart chamber volume both portend heightened risk of age-related heart failure but the gender variations we observed mean men and women may develop the disease for different reasons," says lead investigator.
The differences in size, volume and pumping ability occurred independently of other risk factors known to affect heart muscle size and performance, including body weight, blood pressure, cholesterol levels, exercise levels and smoking.
The research, published in the journal Radiology, is believed to be the first long-term follow-up using MRI showing how hearts change as they age. Previous studies have assessed heart changes over time using ultrasound, but, the researchers say, MRI scans tend to provide more detailed images -- and more reliable information -- about the structure and function of the heart muscle.