This paper investigates the propagation characteristics of terahertz (THz, 0.1-10 THz) and microwave (500 MHz-20 GHz) signals through cardiac tissues to enable nanoscale biomedical diagnostic systems. Using the Double Debye model with parameters extracted from ovine heart tissue datasets, we analyzed spreading, absorption, and total path loss across six representative tissues. Results show that microwave signals experience path loss below 60 dB for 1 mm tissue thickness at 5 GHz, supporting reliable implant-to-skin communication, while THz signals – despite higher attenuation – retain transmittance up to 90% enabling high-resolution, near-field cardiac sensing and communication. These findings establish the complementary use of both frequency bands for future hybrid cardiac monitoring systems.