High-resolution synchrotron X-ray diffraction measurements were performed at 20--46 GPa on CaSiO3 perovskite (Ca-pv) synthesized in a laser heated diamond cell. After heating, we observed peak splittings for the cubic 200 and 211 diffraction lines, attributable to a tetragonal distortion of Ca-pv. The bulk modulus of the tetragonal phase is 255 ¿ 5 GPa for K0T' = 4. The observed intensities and d-spacings of the split lines indicate that the c-axis is shorter than the a-axes (c/a = 0.993 - 0.996). This is compatible with either SiO6 octahedron rotation around the a-axes or SiO6 octahedron distortion (shorter Si-O bonds along the c-axis than the a-axes), provided that the observed phase has a tetragonal unit cell. These structural distortions in Ca-pv can affect its physical properties and capacity for large cations.