The severe repercussions of the latest financial crisis highlighted the crucial role of the financial sector in the propagation of economic and financial shocks. In this paper we analyse the role of financial market frictions in business cycle fluctuations and in the transmission of monetary policy in a small open economy pursuing fixed exchange rate strategy. To this end, we develop and estimate a DSGE model for Latvia with financially constrained households and firms, embedding monopolistically competitive banking sector facing capital constraints. This general equilibrium framework is useful to study the potential of macro-prudential tools and their interaction with other macroeconomic and monetary policy instruments. Our findings suggest that the banking sector mutes the response of bank retail rates to an increase in the foreign policy rate and thus attenuates the drop in real aggregates. A permanent bank capital contraction subdues output, consumption, investment, domestic lending and foreign borrowing in the long run. Under a temporary shock to bank capital, asset prices and housing investment are first to recover, for loans it takes several years, while output, consumption and capital investment rebound at a slower pace. In the long run, a tighter capital requirement leads to higher output, capital investment and domestic lending while reducing household deposits and foreign liabilities of banks.