A valve connector for medical lines of infusion by means of a fluid introducer, comprising: - a tubular body having a cavity, an inlet end adapted for the engagement of an introducer, and outlet end (6, 7), - a hollow pin arranged axially within the cavity of the tubular body and having a closed terminal oriented towards said inlet end of the tubular body and axially distanced therefrom, said hollow pin being in communication with the outlet end (6, 7) of the tubular body and having at least a lateral hole distanced from said terminal for communication with the cavity of said tubular body, and - an elastic sealing element, comprising: - an elastic head having a pre-slotting and normally arranged in a closed condition within said inlet end of the tubular body, in which said pre-slotting is closed, and being axially movable against said terminal of the hollow pin, by effect of the insertion of said introducer into the inlet end, to interact with said terminal assuming an elastically deformed open configuration in which the pre-slotting is opened, - an elastic hollow element joined to said head and interposed between said tubular body and said hollow pin to isolate the cavity of said tubular body relative to said outlet end (6, 7), said elastic hollow element defining an elastic thrust means tending to maintain said head in said closed condition and having an inner surface (23; 26) to contact said hollow pin to isolate said at least one lateral hole relative to the cavity of the tubular body when said head is in the aforesaid undeformed sealing condition, characterised in that: - the terminal of the hollow pin is so shaped as to cause the head of the elastic sealing member assume said open configuration without crossing the pre-slotting, - said tubular body positively presses said inner contact surface (23; 26) of the hollow element of the elastic sealing member against said hollow pin when said elastic head is in the aforesaid closed position, - when said elastic head moves from the closed condition to the open configuration, said inner contact surface (23; 26) of the hollow element of the elastic sealing member opens communication between said at least one lateral hole of the hollow pin and the inlet end of the tubular body through said pre-swotting. - a tubular body having a cavity, an inlet end adapted for the engagement of an introducer, and outlet end (6, 7), - a hollow pin arranged axially within the cavity of the tubular body and having a closed terminal oriented towards said inlet end of the tubular body and axially distanced therefrom, said hollow pin being in communication with the outlet end (6, 7) of the tubular body and having at least a lateral hole distanced from said terminal for communication with the cavity of said tubular body, and - an elastic sealing element, comprising: - an elastic head having a pre-slotting and normally arranged in a closed condition within said inlet end of the tubular body, in which said pre-slotting is closed, and being axially movable against said terminal of the hollow pin, by effect of the insertion of said introducer into the inlet end, to interact with said terminal assuming an elastically deformed open configuration in which the pre-slotting is opened, - an elastic hollow element joined to said head and interposed between said tubular body and said hollow pin to isolate the cavity of said tubular body relative to said outlet end (6, 7), said elastic hollow element defining an elastic thrust means tending to maintain said head in said closed condition and having an inner surface (23; 26) to contact said hollow pin to isolate said at least one lateral hole relative to the cavity of the tubular body when said head is in the aforesaid undeformed sealing condition, characterised in that: - an elastic head having a pre-slotting and normally arranged in a closed condition within said inlet end of the tubular body, in which said pre-slotting is closed, and being axially movable against said terminal of the hollow pin, by effect of the insertion of said introducer into the inlet end, to interact with said terminal assuming an elastically deformed open configuration in which the pre-slotting is opened, - an elastic hollow element joined to said head and interposed between said tubular body and said hollow pin to isolate the cavity of said tubular body relative to said outlet end (6, 7), said elastic hollow element defining an elastic thrust means tending to maintain said head in said closed condition and having an inner surface (23; 26) to contact said hollow pin to isolate said at least one lateral hole relative to the cavity of the tubular body when said head is in the aforesaid undeformed sealing condition, characterised in that: - the terminal of the hollow pin is so shaped as to cause the head of the elastic sealing member assume said open configuration without crossing the pre-slotting, - said tubular body positively presses said inner contact surface (23; 26) of the hollow element of the elastic sealing member against said hollow pin when said elastic head is in the aforesaid closed position, - when said elastic head moves from the closed condition to the open configuration, said inner contact surface (23; 26) of the hollow element of the elastic sealing member opens communication between said at least one lateral hole of the hollow pin and the inlet end of the tubular body through said pre-swotting.