Homo cysteine is a homologue of the protein cysteine, it is a breakdown product of protein synthesis. Homos cysteine is bad for the heart because several research had confirmed that high concentration of homocysteine in the blood contribute to the formation of plaques which leads to the destruction of the arterial walls. The destruction of the heart arterial walls will result in heart diseases.
Also high concentration of homo cysteine in the blood makes the blood to form clots which can easily become lodge in the brain, heart, lungs or in any other organs of the body. This means that high level of homo cysteine in the blood is a risk factor for heart diseases and also stroke in the situation that a clot lodge in the brain.