Abstract: A bypass for power injection includes (a) a housing defining a lumen extending from a proximal end to a distal end coupled to a catheter; (b) a membrane valve mounted within the lumen, the membrane valve having an opening extending therethrough sized to tightly receive therethrough and seal around a power injection device; and (c) a flapper valve extending across the lumen distally of the membrane valve. The flapper valve includes a flap biased toward a closed position in which the lumen is sealed. The flap is rotatable away from the closed position when contacted by a power injection device to permit the device to extend therethrough.