After a long day at the office, an evening spent parked on the couch enjoying your favorite T-V shows might sound like the perfect way to reward yourself and unwind. You’ve earned it, right?

But while some well-deserved R&R does wonders for your mental health, spending too much time in front of a screen can harm your heart.

Too much time sitting — especially if you already are parked in an office for eight hours a day at a desk job — can dramatically increase your risk of heart attack. Even regular exercise can’t cancel out the damage of too much downtime, at work or at home, in front of a screen.

A study published in the Journal of the American College of Cardiology found that couch potatoes who spend over fours a day staring at a screen, compared with those who spend less than two, are more than twice as likely to die or be hospitalized from a major cardiac arrest. Regardless of the usual risk factors like hypertension, smoking, body mass index and inactivity, the study found a forty-eight percent increase in risk from death of any cause and an increase of 125 percent from heart-related mortality.

That means that even office workers who work out after hours are at risk, too.

Who knew sitting could be so dangerous? And why? Scientists point to C-reactive protein, or C-R-P, a chemical found in level twice as high in four-hour screen gazers than those who sit for less than two. This chemical is linked to high-density cholesterol and low-grade inflammation — both signs of a sedentary body.

So how can would-be couch potatoes and desk workers combat sitting sickness? Every hour, get up and walk around for five minutes. Stand up when you’re on the phone, and talk with co-workers rather than e-mailing them. After all, who doesn’t want some more face time with the boss?