Obesity and epicardial adipose tissue (EAT) are linked to heart failure with preserved ejection fraction (HFpEF), contributing to increased filling pressures and reduced exercise capacity. This study investigated whether EAT within the pericardial sac is associated with haemodynamic signs of pericardial constraint. Sixty-four HFpEF patients underwent invasive heart catheterization with simultaneous echocardiography. Right atrial pressure (RAP), right ventricular end-diastolic pressure, and pulmonary capillary wedge pressure (PCWP) were measured. The presence of a square root sign on the right ventricular pressure waveform and the RAP/PCWP ratio were assessed as indicators of pericardial constraint. EAT thickness was measured on echocardiography. Patients with a square root sign had higher BMI, EAT, and RAP compared to those without. Women had more EAT than men despite similar BMI. Women with a square root sign had higher EAT, RAP, and RAP/PCWP ratio. These associations were not seen in men. The study suggests that obesity and EAT are associated with haemodynamic signs of pericardial constraint in HFpEF, particularly in women. The pathophysiological and therapeutic implications of this finding require further study. The study highlights the potential role of EAT in pericardial constraint and suggests sex-specific differences in the association between obesity, EAT, and haemodynamic abnormalities in HFpEF. The findings may have important implications for the management of HFpEF.Obesity and epicardial adipose tissue (EAT) are linked to heart failure with preserved ejection fraction (HFpEF), contributing to increased filling pressures and reduced exercise capacity. This study investigated whether EAT within the pericardial sac is associated with haemodynamic signs of pericardial constraint. Sixty-four HFpEF patients underwent invasive heart catheterization with simultaneous echocardiography. Right atrial pressure (RAP), right ventricular end-diastolic pressure, and pulmonary capillary wedge pressure (PCWP) were measured. The presence of a square root sign on the right ventricular pressure waveform and the RAP/PCWP ratio were assessed as indicators of pericardial constraint. EAT thickness was measured on echocardiography. Patients with a square root sign had higher BMI, EAT, and RAP compared to those without. Women had more EAT than men despite similar BMI. Women with a square root sign had higher EAT, RAP, and RAP/PCWP ratio. These associations were not seen in men. The study suggests that obesity and EAT are associated with haemodynamic signs of pericardial constraint in HFpEF, particularly in women. The pathophysiological and therapeutic implications of this finding require further study. The study highlights the potential role of EAT in pericardial constraint and suggests sex-specific differences in the association between obesity, EAT, and haemodynamic abnormalities in HFpEF. The findings may have important implications for the management of HFpEF.