Viscoelasticity of the Heart: An Overview of Viscoelastic Measurements at Different Scales.

The heart is viscoelastic and exhibits both viscous and elastic behavior with deformation. Cardiac viscoelasticity influences heart function by regulating the volume of blood that can fill, and subsequently be pumped from, the cardiac chambers. Tissue viscoelasticity can also influence cellular functions, motivating the need to measure and model viscoelasticity from the cellular to the organ scale under healthy and disease conditions. Here, we review current protocols, instrumentation, and results from cardiac viscoelastic measurements from the organ to the subcellular level. Since viscoelasticity is regulated by tissue structure and composition, we describe what is known about the viscoelasticity of intracellular and extracellular proteins, cardiac cells, and cardiac tissue, as well as how changes in these proteins with disease progression may influence cardiac viscoelasticity. Finally, we discuss the outlook for the field, including recommendations for standardizing reports of cardiac viscoelastic measurements to increase their utility for biomaterials design for tissue engineering, cardiovascular modeling, and diagnosis.