In general, Heba is an unconditional transfer of property made immediately and without exchange or consideration by one person to another and accepted by or on behalf of the latter.
Heba after death is a kind of heba given during the lifetime of the deceased and becomes valid only after the death of the giver. It must be accepted by the person given the gift and can be revoked during the lifetime of the giver only after approval from the receiver. However, if it was given under duress or deceit or from person who doesn't have the legal capacity or capability to give it, then it can be revoked through court order even if the receiver did not accept the gift. Heba could be given in writing or with witnesses. It is recommended however to have both.
In some special circumstances, heba is one of the advisable ways of getting out of the Sharia succession. However, heba is subject to being contested by the heirs, if it happened within the period where the giver suffered sickness following his or her death regardless of the duration of the illness.
If heba is burdened with liabilities, the receiver could refuse to receive the gift on the ground that it will cause harm to them. In general, receiver can receive the gift or refuse to receive it without need to provide any reason.
There are some legal views stating that since heba can be subjected to revocation by the giver of the gift, it is advisable to put a reasonable consideration to it, this way, the "gift" can no longer be revoked. However, I disagree with this point of view for 2 reasons:
1) If you put money for the purpose of heba, it cannot be considered heba anymore but becomes a sale and purchase process which makes it subject to civil law. This would lead to a new line of argument that can be raised by heirs as they will have the right to object whether the transaction actually transpired or not, especially if the amount paid is small or less than the fair market value of the property given and if the receiver could not prove how they paid the money.
2) In general, that would be considered a fabrication of a process which did not happen and neither the giver nor receiver would like to have such a process. This proposition could subject the receiver to a legal challenge and could prolong the process of transferring property.
Heba given (before death of the giver) has the effect of immediate transfer of property upon acceptance of the receiver while heba given (after death of the giver) has the effect of transferring property only after the condition that the gift will be transferred after death of the giver occurs.