Atherosclerosis was a medical condition in which fatty materials built 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 could eventually lead to heart failure, as blood vessels were 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 urging 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")