[quote=CCC 1450]“Penance requires… the sinner to endure all things willingly, be contrite of heart, confess with the lips, and practice complete humility and fruitful satisfaction.”(emphasis added)
Here the catechism says you must be contrite of heart. It then goes on to further explain this.
[quote=CCC1451]Among the penitent’s acts contrition occupies first place. Contrition is “sorrow of the soul and detestation for the sin committed, together with the resolution not to sin again.”
[quote=CCC1452]When it arises from a love by which God is loved above all else, contrition is called “perfect” (contrition of charity). Such contrition remits venial sins; it also obtains forgiveness of mortal sins if it includes the firm resolution to have recourse to sacramental confession as soon as possible.
[quote=CCC1453] The contrition called “imperfect” (or “attrition”) is also a gift of God, a prompting of the Holy Spirit. It is born of the consideration of sin’s ugliness or the fear of eternal damnation and the other penalties threatening the sinner (contrition of fear). Such a stirring of conscience can initiate an interior process which, under the prompting of grace, will be brought to completion by sacramental absolution. By itself however, imperfect contrition cannot obtain the forgiveness of grave sins, but it disposes one to obtain forgiveness in the sacrament of Penance.
In short a penitent must have at least imperfect contrition for their sins to be forgiven.