This paper develops a Dynamic Stochastic General Equilibrium (DSGE) framework to evaluate the relative importance of the easing of lending and borrowing constraints in mortgage credit markets for business cycle fluctuations in small open emerging economies. Credit markets are characterized by partial dollarization and are subject to demand shocks, innovations to stochastic loan-to-value ratios (borrowing constraints) imposed on borrowers, and supply shocks, innovations to stochastic bank capital-to-asset ratios (lending constraints) imposed on financial intermediaries. In addition, the model features a set of real and nominal domestic shocks to demand, productivity, and fiscal and monetary policy, as well as foreign shocks. The model is calibrated and estimated using data on the Peruvian economy. A historical decomposition conducted on household leverage ratios reveals that these variables’ cyclical dynamics were mainly driven by borrowing constraint shocks or credit demand shifts, while lending constraint shocks played a residual role. Counterfactual simulations also provide evidence in favor of this channel: turning off the borrowing constraint shocks significantly attenuates the fluctuations of leverage ratios from their steady-state levels. The importance of the demand channel in Peru is consistent with mortgage demand-boosting public programs enacted in the 2000s. While applied in the Peruvian context here, the framework is easily adaptable to the historical evolution of credit markets in a large variety of emerging market economies.