The number, specific type, and complexity of percutaneous intracardiac procedures continue to evolve. Many of these procedures require left atrial access using transseptal techniques. These approaches carry with them the potential for pericardial effusion (PE) and cardiac tamponade, particularly in the setting when intraprocedural anticoagulation is being administered. PEs and even cardiac tamponade have been documented with both diagnostic as well as therapeutic procedures. When the effusion is a complication of an intracardiac procedure, it is usually the result of a cardiac perforation. The presentation depends on several factors including the structure that is perforated, the device that caused the perforation, the baseline hemodynamic status of the patient, and the level of anticoagulation present. The incidence has varied substantially although it has been recorded with essentially all intracardiac procedures, both diagnostic and therapeutic on both the right and left side of the heart. Prompt recognition is essential so that prevention of the transition from effusion to tamponade can be attempted (e.g., by reversing anticoagulation) or the hemodynamic collapse can either be averted or treated. Clinical, radiologic, and echocardiographic assessment are each important. Pericardiocentesis can be life-saving and is a core competency for all laboratories performing invasive cardiac procedures. Systems of care must include the knowledge base, equipment, and expert echocardiographic and interventional personnel. Collaboration with noninvasive colleagues and training interventionalists who perform intracardiac interventions, both electrophysiologists and interventional cardiologists, should be required as part of every invasive program.