A device, system, and method for mapping myocardial tissue, such as epicardial tissue on the right ventricle. A system for mapping myocardial tissue may include a mapping device having a distal portion that includes a distal assembly sized and configured to be positioned within the pericardial space. The distal assembly may include an expandable shell, at least one inflatable or expandable element within the expandable shell, and a mapping electrode assembly. Inflation or expansion of the at least one inflatable or expandable element, and therefore expansion of the expandable shell, within the pericardial space may provide sufficient force of the mapping electrodes against the myocardial tissue being mapped. The system may also include a delivery sheath with a retention element for controllably retracting the device within the sheath during delivery and removal of the device from the pericardial space.