Pericardioscopy is a new diagnostic tool to visualize macroscopically alterations in both the epicardium and pericardium. The first experience in 30 patients is reported, after pilot investigations were carried out in experimental animals. After puncture of the pericardial effusion a 9F sheath was introduced under echocardiographic and/or x-ray control. The fluid was removed by aspiration and 100-150 ml of body warm saline were infused in the pericardial sack. A flexible 8F fiberglass instrument (Vantec, Baxter or Storz) and a rigid 110 degree 8F endoscope (Storz) were used for visualization of peri- and epicardium and for video documentation. Complementary to visualization, optically-guided and controlled epicardial and pericardial biopsies were performed and analysed further. Specific diagnosis of pericardial effusion is thus greatly facilitated by the triad, pericardioscopy, cytology and epicardial as well as pericardial biopsy.