Atherosclerosis is a medical condition in which fatty materials - such as cholesterol - build up along the walls of arteries. Over time, these build ups lead to the thickening and hardening of the arteries, calcifying them, resulting in blockage of the artery. The built-up of these plaques can eventually lead to heart failure as blood vessels are no longer able to carry oxygen-rich blood to the heart and other parts of the body.
Benjamin Sisko's father, Joseph Sisko, suffered from progressive atherosclerosis. He had an artificial aorta as a result but despite the urgings of his son and doctors, refused to better take care of himself and even refused to undergo vascular regeneration therapy. In 2372 he eventually suffered a minor stroke brought on by his atherosclerosis. (DS9: "Homefront")