The cells responsible for creating calcium build-up in vessel walls - resulting in heart disease - have now been identified in a new study published in PLOS Biology. Atherosclerosis - or hardening of the arteries - is the main cause of heart disease. It occurs because of calcium build-up in the blood vessels - resulting in hard and narrow arteries. This then leads to problems such as blood flow obstruction and heart issues. Several factors have been known to contribute to the risk of atherosclerosis, however, the cause is not yet known and as of now there is no way to change it once it occurs.