A stretch chamber has been developed in order to visualize the deformation of cells subjected to controlled uniaxial stretch of their substrate. A rectangular, custom-made, transparent silicone channel is used as a deformable substrate. Bovine aortic endothelial cells are plated at the bottom of the channel whose lateral deformation is controlled by two piezoelectric translators. The system is mounted on the stage of a confocal microscope where three-dimensional (3D) images of the cells can be acquired simultaneously in the three RGB channels. The first channel provides images of 216 nm fluorescent beads embedded in the cytoskeleton (used as internal markers). The second is used to image the shape of the nucleus revealed by live cell nucleic acid staining. The third one provides a transmitted light image of the cell outline. 3D images of the cell are taken before deformation, after uniaxial deformation of the substrate (up to 25%) and after relaxation. Results indicate that: (a) the cell closely follows the deformation imposed by the substrate with no measurable residual strain after relaxation, and (b) there is a clear mechanical coupling between the extracellular matrix and the nucleus, which deforms significantly under the applied substrate stretch. Suggesting that the nucleus can directly sense the mechanical environment of the cell, the latter result has potentially important implications for signal transduction.