We consider the Dirichlet problem for the energy-critical heat equation \(\begin{aligned} {\left\{ \begin{array}{ll} u_t=\Delta u+u^5 & \text {in} \quad \Omega \times \mathbb {R}^+,\\ u=0 & \text {on} \quad \partial \Omega \times \mathbb {R}^+,\\ u(x,0)=u_0(x) & \text {in} \quad \Omega , \end{array}\right. } \end{aligned}\) where \(\Omega \) is a bounded smooth domain in \(\mathbb {R}^3\) . Let \(H_\gamma (x,y)\) be the regular part of the Green function of \(-\Delta -\gamma \) in \(\Omega \) , where \(\gamma \in (0,\lambda _1)\) and \(\lambda _1\) is the first Dirichlet eigenvalue of \(-\Delta \) . Then, given a point \(q\in \Omega \) such that \(3\gamma (q)<\lambda _1\) , where \(\begin{aligned} \gamma (q) :=\sup \{ \gamma>0: H_\gamma (q,q)>0 \}, \end{aligned}\) we prove the existence of a non-radial global positive and smooth solution u(x, t) which blows up in infinite time with spike in q. The solution has the asymptotic profile 0.1 \(\begin{aligned} u(x,t)\sim 3^{\frac{1}{4}} \left( \frac{\mu (t)}{\mu (t)^2+\vert x-\xi (t)\vert ^2}\right) ^{\frac{1}{2}} \quad \text {as}\quad t \rightarrow \infty , \end{aligned}\) where \(\begin{aligned} -\ln (\mu (t))= 2\gamma (q) t(1+o(1)),\quad \xi (t)=q+O(\mu (t)) \quad \text {as}\quad t \rightarrow \infty . \end{aligned}\)