This study evaluated a recently developed three-dimensional (3-D) electrocardiographic imaging (3DECI) approach in a closed-chest rabbit model. First, the performance and sensitivity of parameters of 3DECI were evaluated using a geometrically realistic rabbit heart-torso model. Second, a 3-D intracardiac mapping procedure was evaluated based on the heart-torso rabbit model. Third, comparisons were made among the forward-simulated ventricular activation sequence, the activation sequence derived by the intracardiac mapping, and the 3DECI inverse solution. Finally, the present procedures were tested in vivo in a rabbit, in which the relative error between the measured and imaged activation sequence was 0.20 and the localization error was 5.1 mm. The present simulation and experimental results suggest the merits of the 3DECI imaging approach, and the validity of intracardiac mapping as a tool to evaluate the 3DECI. © 2006 IEEE.