An interface for intravascular pressure sensing devices, comprising: a housing; a first input connector configured to receive a distal pressure signal from a distal pressure sensing device; a first output connector configured to output the distal pressure signal over a first communication link to a hemodynamic system in a format useable by the hemodynamic system; a second input connector configured to receive a proximal pressure signal from a proximal pressure sensing device; a second output connector configured to output the proximal pressure signal over a second communication link to the hemodynamic system in a format useable by the hemodynamic system; the first and second input connectors, first and second output connectors, the processor and the display are secured to the housing a processor coupled to the first and second input connectors and to the first and second output connectors, the processor configured to calculate a pressure differential between the distal pressure and the proximal pressure based on the received distal pressure signal and the received proximal pressure signal; and a display in communication with the processor and configured to display proximal and distal pressure waveforms and the pressure differential calculated by the processor; wherein the processor is configured to identify a diagnostic window consisting of a portion of a heartbeat cycle of a patient for performing the pressure differential calculation without administering a hyperemic agent to the patient, the pressure differential being calculated during the identified diagnostic window; and the diagnostic window being selected by identifying the portion of the cardiac cycle corresponding to a time period in which the change in fluid velocity fluctuates around zero. a housing; a first input connector configured to receive a distal pressure signal from a distal pressure sensing device; a first output connector configured to output the distal pressure signal over a first communication link to a hemodynamic system in a format useable by the hemodynamic system; a second input connector configured to receive a proximal pressure signal from a proximal pressure sensing device; a second output connector configured to output the proximal pressure signal over a second communication link to the hemodynamic system in a format useable by the hemodynamic system; the first and second input connectors, first and second output connectors, the processor and the display are secured to the housing a processor coupled to the first and second input connectors and to the first and second output connectors, the processor configured to calculate a pressure differential between the distal pressure and the proximal pressure based on the received distal pressure signal and the received proximal pressure signal; and a display in communication with the processor and configured to display proximal and distal pressure waveforms and the pressure differential calculated by the processor; wherein the processor is configured to identify a diagnostic window consisting of a portion of a heartbeat cycle of a patient for performing the pressure differential calculation without administering a hyperemic agent to the patient, the pressure differential being calculated during the identified diagnostic window; and the diagnostic window being selected by identifying the portion of the cardiac cycle corresponding to a time period in which the change in fluid velocity fluctuates around zero.