Atherosclerosis is the build up of fatty deposits within the arteries. This leads to a blockage of the artery, narrowing the lumen. If this happens to a coronary artery (one supplying the heart with blood) then there is a reduction in blood flow to the heart. This reduces the oxygen supply to the heart, reducing the ability for aerobic respiration to occur. As a result, the heart muscle can die, leading to further problems such as myocardial infarction (heart attack).