Right Heart Diastology, Where Are We Now?

Right heart diastolic dysfunction is increasingly recognized as an early and prognostically relevant process in patients with pulmonary vascular disease, heart failure, and congenital heart disease, among others. Despite this, right heart diastolic dysfunction remains poorly defined and inconsistently measured. This review reframes right heart diastology as a disorder of a unified diastolic unit, integrating right atrial function, right ventricular compliance, and pulmonary arterial load. We synthesize invasive physiology, imaging, and human myocardial data to show that abnormalities in relaxation and compliance commonly precede overt right heart systolic failure and are mediated by load-dependent coupling relationships rather than by isolated chamber dysfunction. Distinct pressure-volume relationships, strong afterload sensitivity, and distinct atrioventricular coupling interactions render left-ventricular paradigms inadequate to understand the right heart. At the molecular level, we examine chamber-specific determinants of right ventricular stiffness, including fibrosis, titin isoform switching, and neurohormonal signaling, grading the evidence across validated, supported, and inferred tiers. We critically appraise available invasive, echocardiographic, and cardiac magnetic resonance indices, highlighting where validation is robust and where extrapolation persists. Finally, we propose a tiered diagnostic data set and a grading framework centered on the right heart diastolic unit, intended to guide future mechanistic studies and prospective clinical validation.