A vasectomy constitutes grave matter. Together with full knowledge of the gravity of the action and full and free consent to the action, a mortal sin is committed. Assuming these conditions were met, the remedy is the same as for any mortal sin: the sacrament of reconciliation, through which a person is restored to a state of grace and may again receive Communion. The Church does not require that a sterilized man attempt to reverse the vasectomy. But if he chooses to do so, he might wish to contact One More Soul, www.omsoul.com.