What materials is a heart valve made of?

Depends. Artificial valves come in two general types - biological and mechanical. Biological valves are usually made from cow or pig tissue. Mechanical valves are made of graphite and metal. Patients on mechanical valves need to be on long term coumadin (warfarin). Not all valves need to be replaced, some may be repaired. Good luck.
See Earlier. Please see my earlier answer regarding heart valves and their function.