Though atrial fibrillation (AF) is a growing public health problem, electrical characterization of the disease with electrocardiography (ECG) is inadequate due to poor spatial resolution. The goal of this study was to investigate propagation of the cardiac activation wave in a healthy swine model using acoustoelectric cardiac imaging (ACI), a noninvasive mapping technology that combines ultrasound with electrical recording to overcome limitations with standard ECG. Real-time 4D ACI with a custom 2D 0.6 MHz matrix US array demonstrated conduction velocities of 2.21 m/s, validated with standard epicardial recording. ACI FWHM at a single timepoint, a measure related to the resolution of ACI in imaging the volume of activation at peak ECG signal, was 7.31 mm, 7.63 mm, and 6.23 mm in the depth, lateral, and elevational directions, respectively. SNR of ACI was 21dB at peak activation. ACI signals tracked through a 4D volume demonstrated appropriate propagation of the signal from base to apex and from endocardium to epicardium. This study demonstrated the potential for this technology to noninvasively map arrhythmias, such as AF, at high resolution.