Nocturnal hypoxemia in daytime normoxemic patients with COPD may lead to an increased right ventricular afterload due to pulmonary hypertension. We investigated the frequency of clinical, electrocardiographical, and radiological signs of right cardiac insufficiency (SRCI) in 178 consecutive COPD-patients [71 bronchitis, 25 emphysema, 82 bronchitis plus emphysema; PaO2 = 60 mm Hg]. Patients with asthma, left ventricular impairment, obstructive sleep apnea syndrome, primary pulmonary hypertension, and neuromuscular diseases were excluded. Polysomnography was performed in all patients. They were divided into 3 groups concerning SRCI: missing, doubtful, and secure SRCI. Parameters of nocturnal pulse oximetry were analyzed within the three groups (Student's t-Test. Chi2-Test. p < 0.05). 25.8% of the patients had secure SRCI without a significant frequency difference between patients with bronchitis and/or emphysema. Patients with secure SRCI had a significant lower mean nocturnal SaO2 than those with missing SRCI (92.7 +/- 2.5 vs. 90.3 +/- 3.5%). With regard to the high prevalence of SRCI in association with nocturnal hypoxemia routine control of nocturnal oxygenation is recommended in daytime normoxemic COPD-patients for the early decision for nocturnal oxygen therapy.