An access tube is used for accessing an anatomic space, such as a pericardial space between the parietal and visceral pericardia. The access tube is advanced against the parietal pericardium and an anchor structure thereon embedded into the parietal pericardium. The access tube can then be used to separate the parietal and visceral pericardia and enlarge the pericardial space. After such enlargement, a needle or other access device can be introduced through the access tube into the pericardial space to provide access for a wide variety of purposes, including aspiration, infusion, and guidewire placement.