Dr. James Blumenthal of Duke University in Durham, N.C., gave heart failure patients a questionnaire to measure depression symptoms such as sadness, irritability and disturbed sleep.
The study participants were then randomly assigned into one of two groups -- usual care and usual care with an exercise routine.
Patients who exercised for 90 minutes a week reduced their symptoms of depression compared with those who just received usual care. However, beyond those 90 minutes, exercise did nothing more, Blumenthal, the study leader, said.
"We do recommend exercise for heart failure patients," Blumenthal said in a statement. "It improves cardiovascular fitness and it also reduces depressive symptoms."
The study was published in the Journal of the American Medical Association.