Acutely ill immobilized patients are at a high risk for thromboembolic events including deep venous thrombosis or pulmonary embolism. Unfractionated heparin (UFH) and low molecular weight heparins (LMWH) are thought to be effective in preventing thromboembolic events. This study is designed to provide efficacy and safety data for thromboprophylaxis with the LMWH certoparin in comparison to thromboprophylaxis with UFH in acutely ill non-surgical patients.

Inclusion Criteria:

• Hospitalization due to an acute non-surgical disease
• Significant decrease in mobility

Exclusion Criteria:

• Indication for anticoagulant or thrombolytic therapy
• Major surgical or invasive procedure within the 4 weeks that precede randomization
• Expected major surgical or invasive procedure (including spinal/peridural/epidural anesthesia or lumbar puncture) within the 2 weeks that follow the randomization
• Immobilization due to cast or fracture of lower extremity
• Immobilization lasting longer than 3 days in the period prior to randomization
• Heparin administration longer than 36 hours in the period prior to randomization
• Acute ischemic stroke

Other protocol-defined inclusion/exclusion criteria may apply