A valve for selectively permitting a fluid flow between first and second medical implements is disclosed. The valve has a housing with an interface suitable for receiving a connector portion of a first medical device such as a catheter, and a seal made of a flexible material. The seal has a first end in fluid communication with the interface, a second end suitable for receiving the second medical device, and at least one slit in fluid communication with the first end and the second end. The slit defines a restricted fluid flow path and a relatively small interior volume when in an undisturbed state, defines an expanded fluid flow path and a larger interior volume upon the introduction of the second medical instrument into the slit, and retracts to define a restricted flow path and a small interior volume upon the withdrawal of the second medical device from the seal.