Constrictive pericarditis (CP) and restrictive cardiomyopathy (RCM) are serious disorders that share common pathophysiologic elements including biventricular diastolic dysfunction, elevated biatrial pressures, and reduced resting cardiac output. Yet, while these 2 disorders have similar clinical presentations, they are caused by very different pathologic processes, which have distinct implications for treatment. CP is potentially curable by surgical pericardiectomy, whereas therapeutic options for RCM are limited. A mistakenly undertaken surgical pericardiectomy in a patient with RCM would be highly inappropriate. Consequently, accurate differentiation between these 2 superficially similar disorders is of paramount clinical importance. The report by Jain et al1 in this issue of JAMA Cardiology describes a simplification of an established technique that aids in distinguishing these 2 groups of disorders.