In　galvanic　coupling　conductive　intracardiac　communication(GCCIC)　of　the　leadless　pacemakers,　the　electrical　signal　transmitted　directly　through　the　myocardium　and　blood　is　inevitably　affected　by　the　cardiac　cycle.　Established　studies　focused　more　on　the　effect　of　the　myocardium.　However,　our　preliminary　in-vitro　experiments　suggested　that　blood　volume　variations　also　significantly　impacted　signal　transmission.　In　this　article,　we　analyzed　the　blood　volume　variations　during　the　cardiac　cycle　and　designed　an　in-vitro　experimental　platform　containing　a　simulated　heart　beating　system　and　an　automatic　channel　characteristic　acquisition　system,　which　controlled　two　peristaltic　pumps　to　realize　the　periodic　blood　volume　variations　and　the　continuous　acquisition　of　channel　gain.　Through　the　in-vitro　porcine　heart　experiment,　the　effect　of　frequency　and　blood　volume　variations　during　the　cardiac　cycle　on　two　channel　gains　was　analyzed.　Considering　the　impact　of　high-frequency　signal　leakage,　the　channel　gain　variations　of　the　low　frequency　are　the　main　concern.　The　results　showed　that　the　channel　gain　was　positively　correlated　with　frequency;　it　changed　periodically　with　blood　volume　variations　in　the　cardiac　cycle,　and　the　trends　were　different　due　to　the　different　signal　paths　of　the　two　channels.　For　the　Right　Ventricle-Right　Atrium　channel,　the　gain　varied　from　-67　dB　to　-53　dB　and　is　inversely　correlated　with　blood　volume.　The　gain　fluctuation　range　was　smaller　for　the　Right　Ventricle-Left　Ventricle　channel,　about　2　dB.　This　study　shows　that　the　gain　of　intracardiac　communication　channels,　especially　the　RV-RA　channel,　is　influenced　by　blood　volume　variations　during　the　cardiac　cycle.　©　2016　IEEE.