Congenital absence of the pericardium is a rare condition,which is frequently missed due its subtle presentation. It may be misdiagnosed as another condition causing right heart dilatation such as an intracardiac shunt. We report the finding of diastolic pressure alternans during cardiac catheterization in this single case report of a patient with congenital total absence of the pericardium. The occurrence of this phenomenon is hypothesized to be due to excessive cardiac hypermobility and paradoxical septal movement. We propose that this finding may be a useful clue to the diagnosis.