The recent financial crisis has renewed the interest of economists, both at the theoretical and empirical level, in developing a better understanding of credit and its mechanisms. A rapidly growing strand of the literature views banks as facing funding restrictions that condition their borrowing to a risk-based capital constraint which, in turn, affects bank lending. This work explores the way banks in Colombia manage their balance sheet and shed slight into the dynamics of credit and leverage over the business cycle. Using a sample of monthly bank balance sheets for the period 1994-2011, we find not only that leverage is predominantly pro-cyclical in the Colombian banking sector, but also that heterogeneiTY matters, and thus, an aggregate measure of bank leverage can mask a fragile financial sector. In addition, although some banks display great dynamics on the right-hand side of their balance sheet during the upward phase of the leverage cycle, changes in the composition of liabilities between core and non-core do not seem to have a clear pattern. Still, more attention should be paid on this by policy makers, as these dynamics could convey information about the phase of the cycle of the economy and the financial vulnerabiliTY of the system as a whole.