A check valve including an elastomeric valve element having a dome-shaped configuration that seals in its at-rest position occluding fluid flow in both directions. The dome-shaped elastomeric valve element is constructed in such a way to be deflectable, such as being activated by the external device such as a male luer whereupon the valve is cracked open to become a two-way valve allowing flow in both directions. The valve element may also be cracked open by sufficient fluid pressure in its inlet. The valve element is self-aligning. The dome-shaped of the valve element includes cut-outs for additional fluid flow, thereby streamlining flow while reducing the potential for air entrapment. The underside of the dome-shaped valve element also includes a thickened concave undersurface and thickened support legs to significantly increase the resistance to high backpressures, while also minimizing potential air entrapment.
