Homocysteine is an amino acid that is often associated with elevated levels and an increased risk of heart disease and stroke. However, there are several synonyms that refer to this molecule, including Hcy, HCYS, and HomoCys. In addition to these abbreviations, homocysteine can be referred to as a thiol-containing amino acid due to its sulfur group, as well as a homologue of the amino acid cysteine. Elevated levels of homocysteine in the bloodstream can be caused by genetic mutations, vitamin deficiencies, and lifestyle factors such as smoking and drinking alcohol. Monitoring and managing homocysteine levels is important for overall cardiovascular health.