Fresh from the "Study finds violent video games do X to kids" pile, we now find — shock — playing them results in "a greater variation in Heart Rate Variability." This isn't straight out one's pulse quickening. HRV is "the oscillation in the interval between consecutive heartbeats" — more or less, a measure of minute changes in heart rate.
The research concludes that violent video games can have effects on your body's autonomous systems, without you even being aware of it. In this instance, kids who played violent games had a greater HRV during sleep but still reported they'd slept fine. Makes sense. Games can have effects on your voluntary systems beyond your control, too. Like Dead Space making you shit your pants.
There's debate on whether HRV means anything, but the researchers indicate they're going to use this research to study links between violent video games and aggression and, of course, "video game addiction."