To employ a ventricle device with a limited capacity which is expanded per critical continuation period and in a process of changes in capacity at any critical time by aiding a pump function of the heart without inducing the elongation of a ventricle wall in a ventricle aid system for normal cardiac action.

An inner chamber 15 for the ventricle with the maximum capacity of 30 ml is inserted into a ventricle 10 of a disordered heart, and a controller and a battery cell are provided. The controller and the battery cell are so arranged that the expansion and contraction of the chamber are repeated to match the beating of the heart, namely, the pulsation thereof and the degree of expansion is gradually reduced to match the degree of the restoration of the heart and can be finally removed. The patient may fall into a critical condition for any unexpected reason, whether the controller operates or not. A fail- safe function is prepared and performed for such a case to ensure a higher rate of revival as compared with the method for replacing the heart totally with an artificial heart.