Abstract: A medical device system comprising a guide catheter and a leaflet fastening applicator, the guide catheter having suitable dimensions for deployment and insertion percutaneously into a human heart in a vicinity of a heart valve, the leaflet fastening applicator having a size allowing insertion through the guide catheter and being capable of holding portions of opposing heart valve leaflets, wherein the fastening applicator comprises a pair of grasping-electrodes adapted for holding and engaging the portions of opposing heart valve leaflets together and for applying energy to fasten the portions, in which heart valve leaflets can be captured and securely fastened, thereby improving coaptation of the leaflets and improving competence of the valve.