The main adverse effects of ACE inhibition can be understood from their pharmacological action. The other reported adverse effects are liver problems and effect on the fetus. Kidney problems may occur with all ACE inhibitors that directly follows from their mechanism of action. Patients starting on an ACE inhibitor usually have a modest reduction in glomerular filtration rate (GFR). However, the decrease may be significant in conditions of "pre-existing" decreased renal perfusion, such as renal artery stenosis, heart failure, polycystic kidney disease, or volume depletion. In these patients, the maintenance of GFR depends on angiotensin-II-dependent efferent vasomotor tone. Therefore, renal function should be closely monitored over the first few days after initiation of treatment with ACE inhibitor in patients with decreased renal perfusion. A moderate reduction in renal function, no greater than 30% rise in serum creatinine, that is stabilized after a week of treatment is deemed acceptable as part of the therapeutic effect, providing the residual renal function is sufficient.