Researchers from Stockholm University, Uppsala University and the Karolinska Institute tested 19 boys aged 12 to 15 while playing one violent and one non-violent video game.

Lead researcher Frank Lindblad of Stockholm University said the study found the boys had irregular heart rates after they were finished playing the violent game, The Local newspaper reported Friday.

"What we saw was irregular rhythms with variations in the distances between beats," Lindblad told the newspaper.

He said the findings suggest violent video games have a marked influence on the nervous system of young gamers and raises concerns about the effect on their central physiological systems.