Propagation of radio-frequency signals inside human body is demanding to analyze as it is a highly complex medium consisting of different frequency-dependent lossy materials of varying thickness. Moreover, experimental analyses are also unfeasible because that requires probes to be placed inside a human body to collect the signals. This paper focuses on in-body to in-body implant communication for future multinodal capsule-like leadless cardiac pacemaker technology. The frequency range of 0.3-3 GHz is analyzed using very detailed numerical simulations of digital human models. The results show that the Industrial, Scientific, and Medical radio band of the frequency range of 2.4-2.5 GHz is optimal, having the least attenuation of signals considering the size constraints of the implant antenna. Furthermore, the placement of an additional subcutaneous implant transceiver is studied. The analysis shows that the abdominal wall is the optimal position for the placement of the implant compared to shoulder and lateral side of the body. This result is further validated by an in vivo experiment on an adult pig. The other novelty of the study is the investigation of the channel behavior based on ventricular blood volume of the heart to find out the appropriate timing of the transmission of signals between the implants. The results show that the attenuation of the signal increases with the increase in blood volume inside the heart.