This paper presents a real business cycle model with financial frictions and two credit markets to investigate the qualitative and quantitative relevance of credit market heterogeneity. To address this line of inquiry we contrast the transmission of financial shocks in an economy where loans are the only form of credit to one in which both loans and bonds exist. We estimate the model using Bayesian methods over the sample period 1985Q1 { 2015Q1 for the U.S. economy. We find that credit market heterogeneity plays an important role in attenuating the impact of financial shocks by allowing borrowers to substitute away from the affected credit market. The shock attenuation property of credit market heterogeneity works through asset prices and substitution toward alternative credit types. Bank balance sheet linkages reduce the shock attenuation effect associated with heterogeneous credit markets. The origination of financial shocks can influence both the size and the persistence of their impact.