The cause of dyspnea may remain uncertain even after a complete non-invasive clinical workup, and a right heart catheterization is performed to achieve a definitive diagnosis. Although pulmonary artery wedge pressure (PAWP) is key for the differential diagnosis between pulmonary arterial hypertension (PAH) and heart failure with preserved ejection fraction (HFpEF), the diagnosis may be challenging because PAWP may be normal after diuretic administration in HFpEF patients on optimal medical therapy. In order to avoid misdiagnosis, building a pre-test probability of pre- or post-capillary pulmonary hypertension is crucial. Current guidelines on pulmonary hypertension suggest to interpret hemodynamics in the context of clinical picture and imaging, mainly echocardiography. Indecisive measurements of PAWP in patients with an intermediate to high clinical probability of HFpEF can be repeated after a fluid challenge test with rapid infusion of 7 ml/kg or 500 ml of saline. The procedure is simple and does not take much catheterization laboratory time. A post-fluid challenge PAWP >18 mmHg strongly supports the diagnosis of occult HFpEF. A possible alternative to fluid challenge test is exercise or dobutamine stress test. However, exercise hemodynamics is not feasible in all catheterization laboratories and may be difficult to interpret due to wide swings in intrathoracic pressures. Otherwise, dobutamine infusion during right heart catheterization may be potentially more practical than exercise stress, but requires further validation studies to determine its utility. The aim of this case report is to provide a practical roadmap for challenging cases, when the differential diagnosis between PAH and HFpEF is uncertain.