Have you ever heard of stiff heart syndrome? Known clinically as cardiac amyloidosis , this condition mimics other heart health problems and, as a result, is often overlooked and untreated—which could lead to serious and even deadly complications. Here's what you need to know about cardiac amyloidosis. What is cardiac amyloidosis? Cardiac amyloidosis occurs when abnormal proteins called amyloid build up in the heart. As the amyloid proteins accumulate and start to replace healthy heart tissue, the heart begins to have a harder time working properly. Over time, this can cause the heart to