There are few studies on the influence of different doses of intravenous nitroglycerin (NTG) on the appearance of drug tolerance.A controlled clinical trial was performed in 40 patients admitted to an ICU with the diagnosis of acute myocardial infarction (AMI). The patients were divided into two groups: group A with a continuous perfusion of NTG at 2 mg/h, and group B with 4 mg/h. At 30 minutes of the infusion, NTG was exchanged for a placebo in half of the patients of each group (subgroups A1 and B1) with the remaining patients continuing with NTG for 24 h (A2 and B2). The hemodynamic variables studied were central venous pressure (CVP), pulmonary capillary pressure (PCP), mean pulmonary artery pressure (PAP) and mean blood pressure (BP).The patients in group A showed a decrease in the hemodynamic effects in all the variables studied. At 24 h of infusion no differences were observed with respect to the previous NTG values for CVP and PCP, with significant differences being maintained for PAP and BP. In group B the hemodynamic effect was maintained for all the variables during the 24 hours studied.In patients with acute myocardial infarction, the dosis of nitroglycerin administered was found to have a determined influence in the appearance of drug tolerance with this fact being more evident on evaluation of the effect of nitroglycerin on the venous system.