In this paper, we analyze the performance of dual-hop channel state information (CSI)-assisted amplify-andforward (AF) cooperative networks using orthogonal space-time block codes (OSTBCs) over independent but not identically distributed Nakagami-m fading channels. Specifically, we present closed-form expressions of the outage probability (OP) and the symbol error probability (SEP). The analytical results are given in tractable forms which readily allow us to assess the performance of AF relay systems using OSTBCs. For sufficiently large signal-to-noise ratio, we obtain the asymptotic results for OP and SEP which reveal insights into the effect of fading factors on the diversity and coding gains. It has been shown that between the two hops the more severe link solely determines the diversity and coding gains. In particular, these two gains strictly depend on the fading severity parameters and the channel mean powers of the more rigorous hop, respectively. Numerical results are provided showing an excellent agreement between our analytical results and those of Monte-Carlo simulations for selected scenarios.