Transthyretin amyloid cardiomyopathy, also known as ATTR-CM, is a type of cardiomyopathy which is underdiagnosed and potentially fatal.In ATTR-CM, a protein called transthyretin, which circulates in the bloodstream becomes misshapen and builds up in the heart, nerves and other organs. When this protein builds up in the heart, the walls of the heart become thickened and stiff. The stiff heart is unable to relax properly to fill with blood and becomes inefficient in pumping blood to rest of the body. As the condition progresses, the heart pumping function weakens. This results in heart failure, where the heart is unable to pump sufficient blood to meet the needs of the body.