This article demonstrates a confidential data vulnerability in integrated circuits, especially in System-on-Chip (SoC)-field programmable gate array (FPGA). We demonstrate that the electromagnetic (EM) emanations of internal Advanced eXtensible Interface (AXI) standard data bus are exploitable. Electromagnetic pulses recorded by a near-field probe in the vicinity of such data bus can be mapped to the underlying data flux, just as an electrocardiogram (ECG) would map the heart activity and blood circulation. This vulnerability is demonstrated by spying on the EM emanations caused by internal bus while MNIST handwritten digit images are sent through them. The transmitted MNIST data are found to be framed by pre-amble and post-amble signals enabling the detection of transmitted data themselves. Data (images, in this paper) are then reconstituted by using a simple algorithm. © 2023 IEEE.