We used a total internal reflection fluorescence microscope based on the near field optics principle to study the Ca2+ signals in single heart cells of Sprague-Dawley rat. Due to the high signal to noise ratio and high speed of data acquisition of this microscope, the Ca2+ images show complex 2-dimensional wave patterns. The local elementary Ca2+ release units play important role in the formation and transformation of Ca2+ wave. Simulations based on Fire-Diffuse-Fire model show that the Ca2+ wave, composed of Ca2+ release units, may steadily exist in single heart cell. Our results will be helpful for understanding the micro-dynamics of living excitable medium.