To compare renal function (51Cr-EDTA clearance) 48 hours post open-heart surgery (coronary bypass or valve surgery) in patients with impaired renal function after randomization to either nifedipine infusion at start of surgery and the following 24 hours or placebo (0.9% saline infusion). Study hypothesis is that nifedipine has a prophylactic effect on decline in renal function.

Inclusion Criteria:

1. Patients of either gender above 18 years of age.
2. Patients with significant coronary stenosi(e)s (≥ 75% coronary artery lumen surface stenosi(e)s and / or aortic- or mitral valve vitriuim that are accepted for coronary artery bypass surgery and/or valve replacement surgery.
3. Patients with impaired renal function, defined as increased serum- creatinine. Men: ≥ 150 µmol/l and Women: ≥130 µmol/l.

Exclusion Criteria:

1. Patients on maintenance hemodialysis
2. Renal transplant patients
3. Patients with ejection fraction ≤ 35%
4. Patients with unstable angina pectoris