We study the problem of existence of conformal metrics with prescribed scalar curvatures on a closed Riemannian \begin{document}$ 4 $\end{document} -manifold not conformally diffeomorphic to the standard sphere \begin{document}$ S^{4} $\end{document} . Using the critical points at infinity theory of A.Bahri [ 6 ] and the positive mass theorem of R.Schoen and S.T.Yau [ 32 ], we prove compactness and existence results under the assumption that the prescribed function is flat near its critical points. These are the first results on the prescribed scalar curvature problem where no upper-bound condition on the flatness order is assumed.