Suppose $\pi$ is a finite dimensional representation of $C^*$ algebra $A$ on a Hilbert space $H$,then $\pi$ is the direct sum of finite dimensional irreducible subrepresentations.
My quesion is :If $\pi$ is an infinite dimensional representation of $C^*$ algebra $A$ on a Hilbert space $H$ with dim($H$)=$\infty$.Does there exsit a finite dimensional representation of A on $H_0$,where $H_0$ is a subspace of $H$?Can we decompose the infinite dimensional representation?
Not necessarily. Take $A=B(H)$, and $\pi$ the identity representation.
More generally, take $A$ any C$^*$-algebra with $\pi$ an infinite-dimensional irreducible representation (easy examples of such $A$ are $K(H)$ and UHF$(2^\infty)$). This $\pi$ cannot have summands, since $\pi(A)'=\mathbb C$.