If you accept Christ into your heart, then you will be saved. That means that you acknowledge Jesus died for your sins, that he rose again and sits on the throne right now, and Jesus can give you a new heart if you follow after him and obey his commands. Building a new heart will always be work in progress, and even if you falter God will still love you. Sinning after you've accepted Christ won't revoke your entrance to heaven, not if you sincerely believe that Jesus is your savior. The Bible doesn't say "Believe on the Lord Jesus Christ, and remain perfect until you die, and then you will be saved." It says "Believe on the Lord Jesus Christ and you shall be saved."