Ultrasound current source density imaging (UCSDI) is a noninvasive method for mapping electrical current based on the acoustoelectric (AE) effect. This technique can potentially overcome the limitations (i.e. poor resolution, inaccurate anatomical registration) of the conventional electrical mapping procedures typically used during treatment of sustained arrhythmias. In this study, UCSDI of the electrocardiogram (ECG) is demonstrated using a clinical electrophysiology catheter placed on the epicardium of the live rabbit heart. For the first time, 3-D cardiac activation maps are presented. Activation maps were used to calculate the cardiac conduction velocity for atrial pacing (1.31 m/s). We also demonstrated multi-electrode UCSDI for improving mapping accuracy by reducing the lied-field effect. This study indicates that UCSDI is potentially capable of real-time 3-D mapping of the cardiac activation wave, which would greatly facilitate ablation procedures for treatment of arrhythmias.