A prosthetic heart valve provided herein can include a porcine small intestine submucosa (P-SIS) tissue leaflet. The P-SIS tissue can include multiple stacked layers that are tensioned and cross-linked to form a material having a thickness of between 50 microns and 0.33 mm. In some cases, a prosthetic heart valve can include a plurality of leaflets secured together and retained within the expandable tubular member.