My wife will have a heart surgery and may need to change the valve of her heart. There are two options: a valve from a pig or a mechanical valve. If she takes the mechanical valve, then she will have to use medication for the rest of her life and this medication would causes great harm to the baby if she were to get pregnant. We do not have any kids yet. Is it allowed for her to get a valve from a pig?

All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

It is known that the pig is ritually impure. The basic principle is that it is prohibited for the Muslim to use its heart valve or any part of it to be transplanted into a human body because this would entail having an impure part inside the body permanently, which accordingly necessitates the invalidity of the prayers and all acts of worship that require ritual purity. However, if the patient has no pure alternative and the only remedy for his condition is a part from an impure animal, then there is no harm in transplanting it. Allaah, The Exalted, says (what means): {But whoever is forced (by necessity), neither desiring (it) nor transgressing (its limit), there is no sin upon him.} [Quran 2:173]

An-Nawawi wrote:

"If his bone gets broken, then he should mend it with a pure bone (taken from a pure animal). Our companions (from the Shaafi‘i School) said, 'It is unlawful for him to mend it with an impure bone as long as he can use a pure one; otherwise, he has a valid excuse. However, if he does not need it or if he finds a pure substitute yet he chooses the impure bone, then he has committed a sin and must remove the impure bone unless this would cause harm or damage to a body organ or imperil his life.'" [Al-Majmoo‘]

You mentioned that there is an alternative, namely the mechanical valve. The basic principle is that you should opt for the mechanical valve instead of the heart valve from the pig unless the potential harm that you mentioned would be inevitable according to the opinion of trustworthy doctors and there is no way to avoid it. In this case, we believe that there would be no harm in using the pig valve given the necessity, as indicated by the Quranic verse cited above.

Allaah knows best.