Fifty % of patients with signifcant Heart Disease demonstrate sleep apnea. With the sleep apnea, the blood is not properly oxygenated nor circulated. Significant bradycardia (slowing of the heart rate) occurs during in 95% of apnea episodes. With all of this, the corornary arteries can't properly oxygenate and support the heart, and hence high risk for heart attack.
A recent study revealed what has always been suspected. Sleep apnea decreases blood flow and oxygen to the brain, elevates blood pressure within the brain and eventually severely affects the brains internal ability to control these changes and prevent damage to itself. Result, high risk for stroke.