Growing up poor might put you at risk for heart failure in adulthood, a new study suggests.

Heart failure, a progressive condition, means the heart isn't pumping as well as it should. This causes fatigue and shortness of breath, and can make everyday activities difficult to carry out.

Finnish researchers looked at household income for hundreds of children in 1980. The findings showed that kids from poor families were more likely than richer children to have an enlarged, poorly functioning lower left heart chamber -- a sign of heart failure -- three decades later.

The results aren't surprising, health experts say.

"There are continuing socioeconomic inequalities in health across generations and across countries," said Rebecca Hardy, from the Institute of Epidemiology and Health at University College London in England.

Hardy, who is with the Lifelong Health and Aging unit, added that poverty "has shown to be consistently related to cardiovascular disease and other health outcomes in adulthood." These associations cannot be entirely explained by adult employments and earnings, she said.

Although it isn't clear how low income might lead to heart damage, she said obesity, poor health habits or the emotional environment within the family could play a role.

The study can't actually prove that poverty led to poor heart health, but this association remained even after researchers took into account age, sex, standard risk factors for heart disease, and participants' earnings as adults, the researchers said.

More research is needed to find the best ways to target these income and health inequalities, as they may vary from place to place, noted Hardy, who wrote an editorial accompanying the study.

She voiced a note of caution, however. While evidence suggests it's important to target these gaps early in life, she said, "we need to be careful that interventions aimed at improving the health across the whole population do not, inadvertently, increase inequalities."

Dr. Byron Lee is a professor of medicine at the University of California, San Francisco.

"There is something about being poor during childhood that leads to a thickened, impaired heart 30 years later," said Lee.

The next step is to figure out the exact cause, he said. "Is it childhood diet, stress or other environmental factors? Currently, this is unknown," according to Lee.

The study was led by Dr. Tomi Laitinen, from the University of Turku's research center of applied and preventive cardiovascular medicine. His team collected data on nearly 1,900 people who took part in the 1980 and 2011 Cardiovascular Risk in Young Finns Study.

Annual family income was reported at the start of the study for kids aged 3 to 18. Later, participants were evaluated for left ventricular size and left ventricular function when they were between 34 and 49 years old.

An enlarged left ventricular is associated with heart failure, and left ventricular dysfunction can be a predictor of heart failure, the researchers noted.

In the United States, about 5.7 million adults have heart failure. And about half will die within five years of diagnosis, according to the U.S. Centers for Disease Control and Prevention.

The authors acknowledged some limitations to the study. For one, participants' heart function was not assessed during childhood. In addition, the researchers couldn't tell at what point during childhood family economics started to affect heart function.

Because all of the participants were white, it's not clear if poverty could affect children of other backgrounds, the study authors said.

Dr. Jefry Biehler, chairman of pediatrics at Nicklaus Children's Hospital in Miami, said that "this is another study that shows that socioeconomic status plays a bigger role in the outcomes of lives and of health than people suspected in the past."

Biehler explained that researchers "need to find the causes before we can even come close to deciding how we can prevent these diseases and improve the outcome in children across all economic groups."

The report was published online June 26 in the journal JAMA Pediatrics.