A prosthetic heart valve can have one or more hermetic layers. The inner skirt and/or the outer skirt can comprise one or more hermetic layers, or the entire valve frame can be encapsulated within one or more hermetic layers. Each hermetic layer can be substantially nonporous or can have pores therein that are sized to discourage cellular ingrowth. The hermetic layer can prevent ingrowth of surrounding native tissue, thereby reducing pannus formation on the prosthetic leaflets. Alternatively or additionally, shapes of the leaflets of the valvular structure of the prosthetic valve and/or the coupling of the leaflets to the valve frame can be selected to avoid the incidence of stasis when implanted at a relatively low pressure gradient hemodynamic location. Such a prosthetic heart valve may reduce the risk of thrombosis.