Conductive Intracardiac Communication (CIC) uses cardiac tissue as a transmission medium for short-range wireless communication and is a potential method for enabling leadless multi-chamber pacing. However, the characterization of the intracardiac channel is significantly influenced by the experimental setup and conditions. The reported results in the literature vary depending on the measurement methods used, posing challenges in obtaining reliable channel characterization for CIC. In this paper, we aim to investigate the effects of different measurement devices and conditions on the intracardiac channel. By clarifying how impedance imbalance affects the gain measurement results, we design a weak-signal measurement circuit with high common-mode rejection. This new circuit provides a more accurate and effective gain measurement scheme for the CIC channel. An equivalent circuit model simulating cardiac biomechanical impedance is constructed to analyze how capacitive and resistive imbalances affect the gain measurement results. The effects of these imbalances are verified by intracardiac channel impedance imbalance experiments. A high common-mode rejection-high-resistance differential measurement circuit that can reduce the effects of capacitive and resistive imbalances simultaneously, is then designed to suppress the interference in the experiments. The results show that changes in the measurement equipment and isolation method lead to variations in the coupling circuit characteristics, causing differences of up to 16.65 dB in the measurement results. Experiments using the designed measurement circuits effectively mitigate interference from impedance imbalance on the measurement results. This study identifies the reasons behind the discrepancies in the experimental results of previous studies and provides a more reliable gain measurement scheme for CIC research.