Background: Contrast induced nephropathy (CIN) is an important complication of cardiac catheterization. Adequate hydration is the simplest and most effective way of protecting renal function. This study was designed to determine whether left ventricular end diastolic pressure (LVEDP). Guided hydration would be superior to routine hydration in patients at risk for CIN undergoing cardiac catheterization. Methods: Prospective randomized trial including 200 patients at Alexandria main university hospital. Laboratory investigation: Serum urea, creatinine, eGFR by the MDRD equation, Echocardiographic measurement of the left ventricular filling pressure (LVFP) using the ratio (E/septal è). LVEDP measured systematically (in mmHg) using a pigtail catheter. Patients were randomized in a 1:1 fashion to either LVEDP-guided hydration (group 1) or standard hydration (group 2). The primary endpoint was 25% or 0.5 mg/dl or more increase in SCr (two values measured on days 1 and 4), the secondary endpoints were major adverse events (death, myocardial infarction and dialysis) occurring within 30 days. Results: We found statistically significant difference between the two types of hydration regarding the occurrence of the primary endpoint (p = 0.046). We found no statistically significant difference between the two groups regarding the secondary endpoints. Statistically significant correlation was found between LVEDP prior to contrast administration and that at the end of the procedure (p