High levels of stress combined with depression increase the risk of heart attacks and death according to a new study published in the journal Circulation: Cardiovascular Quality and Outcomes.

Overall, the study found that patients with both conditions are nearly 50 percent more likely to experience a heart attack as a result of heart disease or die than patients without low depression or stress, according to Time.

The lead author, Carmelia Alcantara of Columbia University Medical Center in New York City, stated that the combination of high depression symptoms and high stress can be “particularly harmful” to those in an “early vulnerability period” of heart disease. Alcantara and the other researchers who studied the effect of deep depression and stress on 4,500 patients called the pair the “psychosocial perfect storm.” The researchers followed patients ages 45 or older with coronary heart disease, or plaque buildup in the arteries, which is the most common type of heart disease.

The study’s participants had in-home examinations along with stress and depression questionnaires from 2003-2007. Nearly 12 percent of participants had high stress, 14 percent reported having high depression and 6 percent had both, according to Reuters. After six years, 1,337 patients died or had a heart attack. Risks were not increased over longer periods or for people with either depression or stress, but not with those with both.

Alcantara said that the researchers were “surprised” that high depression and high stress alone did not increase the risk of another heart attack or of death. She added that more research is needed to determine why “psychosocial factors” are tied to heart health. Behavioral depression and stress management therapies could aid in improving heart disease patients’ fates, but Alcantara said that more research needs to be completed on that matter as well.

Although past research has suggested that depression and stress have been associated with increased risks for heart patients, this study did not find a cause-and-effect relationship between the two.

Coronary heart disease is the leading cause of death in the U.S. for women and men, according to the National Institutes of Health.