Researchers have reported couch potatoes who spend more than four hours a day sitting passively in front of a screen have roughly a 125 percent greater risk of developing symptoms of cardiovascular disease, such as angina (shortness of breath) or experiencing a heart attack than their peers who only spend about two hours doing so [source: Levine].
Sitting is clogging your heart. Excessive sitting changes the way your body handles fats (known as lipids) in your blood, and the outcome isn't good. It puts the brakes on HDL production; HDL is known as the good cholesterol because it cleans up the bad cholesterol, LDL, which builds up on the walls of your arteries. Researchers have associated all that sitting you're doing with lower amounts of HDL circulating in your body, and that means lipids and triglycerides are allowed to build up -- and that fat in your blood puts you at a greater risk of developing cardiovascular disease [source: Berkowitz and Clark].