An intracardiac defibrillation catheter system used for defibrillation by applying direct voltage synchronously with R waves of an electrocardiogram only when extrasystole and other unusual situations do not occur is provided. The intracardiac defibrillation catheter system is provided with a defibrillation catheter, a power source device, and an electrocardiograph. The power source device is provided with: a DC power source unit (71)； an external switch (74) of an energy applying switch 744； and an arithmetic processing unit (75) which controls the DC power source unit. The arithmetic processing unit controls the DC power source unit in the following manner that: events deducing that the electrocardiogram input by the electrocardiograph is an R wave is sensed gradually, and when the polarity of the sensed event (Vn) after the input of the energy applying switch, the polarity of the former sensed event (Vn-1) and the polarity of the antepenultimate event (Vn-2) accord, direct voltage is applied to a number 1 DC electrode group (31G) and a number 2 DC electrode group (32G) synchronously with the event (Vn).本發明提供一種僅在期外收縮等異狀未發生時與心電圖的R波同步地施加直流電壓來進行除顫的心腔內除顫導管系統。該心腔內除顫導管系統具備除顫導管、電源裝置以及心電計，電源裝置具備DC電源部(71)、包括能量施加開關744的外部開關(74)、控制DC電源部的運算處理部(75)，運算處理部以如下的方式控制DC電源部，即：逐次感測根據從心電計輸入的心電圖推斷為R波的事件，並在能量施加開關的輸入後被感測到的事件(Vn)的極性與之前一個被感測出的事件(Vn-1)的極性以及之前二個被感測出的事件(Vn-2)的極性一致時，與該事件(Vn)同步地對第一DC電極組(31G)以及第二DC電極組(32G)施加直流電壓。
