To study cardiovascular tissue mechanics it is desirable to use simplified model systems that closely resemble native tissue composition. Bioartificial tissues, consisting of single cellular and matrix (e.g. collagen) components, provide a 3-D environment for cells that is easily modified and quantified. We have developed uniaxial cyclic stretching tests that allow us to identify cell and matrix contributions to the overall tissue force. Ring shaped tissues are fabricated with cardiac fibroblasts or vascular smooth muscle cells and tested on a custombuilt uniaxial tester with computerized displacement control and continuous force monitoring. Tissue forces during cyclic stretch are nonlinear and viscoelastic and after many cycles the peak tissue forces are similar at different magnitudes. To investigate how cells and matrix contributed to the tissue force, we added Cytochalasin-D before or during cyclic stretch to disrupt the actin cytoskeleton. Cytochalasin-D eliminates the cell force contribution while leaving the matrix contribution. We subtract this matrix contribution from the tissue force to calculate the cellular contribution. Our results show that cell behavior is linear viscoelastic up to 25% stretch, but the slope of the force-stretch curve is lower at high amplitudes. The matrix component is highly nonlinear, and peak force amplitude increases with stretch.