Continuing the analogy of heart muscle as being like a wall, the extracellular matrix is the mortar which surrounds the cardiomyocyte and fibroblasts bricks. The matrix is composed of proteins such as collagen and elastin along with polysaccharides (sugar chains) known as glycosaminoglycans.[1] Together, these substances give support and strength to the muscle cells, create elasticity in cardiac muscle, and keep the muscle cells hydrated by binding water molecules.