Pulmonary hypertension (PH) is a rare disease, which is characterized by an increased pressure and resistance in the pulmonary circulation. If left untreated it has severe outcomes and can lead to right heart failure. PH is haemodynamically divided into a pre- or post-capillary form. To differentiate between pre- and post-capillary PH the mean pulmonary artery wedge pressure (mPAWP) has to be measured by right heart catheterization (RHC). The proper distinction between pre-capillary and post-capillary PH may be challenging, because the measurement of mPAWP is prone to many error sources and interobserver variability. Additionally, in some cases, in regard to post-capillary PH, under certain circumstances (extensive use of diuretics) the mPAWP can be decreased. This can lead to misclassifications between pre- and post-capillary PH. To resolve this issue, fluid-challenging during right heart catheterization is popular. This clinical practice already shows, that mPAWP correlates to a certain degree with the patient´s volume status. Furthermore, overhydration is a common state in patients, especially in heart failure, which exacerbates symptoms and cardiovascular function. Therefore, the focus of this study was to determine the influence of overhydration on haemodynamic pressures, especially the mPAWP. To investigate this, a patient collective (n=252) were examined using Body Composition Monitor quasi-simultaneous with right heart catheterization to measure following parameters: OH in [L], OH in [%], mean pulmonary artery wedge pressure (mPAWP), mean pulmonary artery pressure (mPAP), mean right atrial pressure (mRAP) and cardiac output (CO) by thermodilution. Comparative and correlative analyses were conducted using these values. The results of the comparative analyses showed that patients with an mPAWP >15 mmHg are more overhydrated than patients with an mPAWP ≤15 mmHg. In addition, it was displayed that a negative volume status is associated with lower mPAP-, mRAP-, and mPAWP and a positive volume status with higher pressures. In contrast, the results of the correlative analyses showed, that the relationship between overhydration and mPAWP is very weak. Due to this, overhydration should not be used as a parameter to interprete mPAWP.