A medical device at least partially insertable into a patient. The device comprises a catheter portion comprising a flexible tube that is at least partially insertable into the patient, and a valve portion proximal to the catheter portion. The valve portion comprises a planar flexible member comprising first and second valve portions separated from one another by an internal slit. The thickness of the planar flexible member at the internal slit is less than the thickness of the planar flexible member at any other location.
