  In this paper we study the small time asymptotic behavior of the spectral
heat content $\widetilde{Q}_D^{(\alpha)}(t)$ of an arbitrary bounded $C^{1,1}$
domain $D$ with respect to the \textit{subordinate killed Brownian motion} in
$D$ via an $(\alpha/2)$-stable subordinator. For all $\alpha\in (0,2)$, we
establish a two-term small time expansion for $\widetilde{Q}_D^{(\alpha)}(t)$
in all dimensions. When $\alpha\in (1,2)$ and $d\geq 2$, we establish a
three-term small time expansion for $\widetilde{Q}_D^{(\alpha)}(t)$.
