A cardiovascular device (11), adapted to be fitted into a cardiac ventricular cavity (2) having a volume with blood flowing therethrough, which is bounded by walls (8) and has a larger longitudinal dimension (D1) and a smaller transverse dimension (D2), characterized in that it comprises diaphragm means (16) that can be disposed in said ventricular cavity (2) substantially transverse to said larger longitudinal dimension (D1), in such an arrangement as to reduce said volume, said diaphragm means (16) having a peripheral edge (15) which can be sealingly engaged with said walls (8) and being adapted to be alternately driven between an active blood pushing displacement and an inactive return displacement.
