Careful invasive assessment of pulmonary hemodynamics is essential in the evaluation of PH. The key components of this test are listed in Table 3. Although this is the gold standard, there are several potential errors. Hemodynamic measurements should always be taken at end-expiration. Additionally, inaccurate measurement of PAOP may lead to misclassification of a high proportion of patients as having PAH when, in fact, simultaneous measurement of the LVEDP confirms the presence of PVH. In patients in whom there is a high suspicion of left-sided heart disease, a direct measurement of LVEDP may therefore be needed. Finally, cardiac output (CO) is often measured by thermodilution. However, tricuspid regurgitation is quite prevalent in those suspected of having PH; thus thermodilution may underestimate CO, and a Fick determination of CO may be required. If there is a suspicion of HFpEF as a cause of PH, but values of PAOP are normal or borderline, exercise can be performed in an attempt to unmask dynamic elevations in PAOP that occur when CO increases and diastolic filling time is further reduced at higher heart rates. Volume loading (eg, 250-500 mL of normal saline given as a bolus) can also be performed for the same purpose; however, exercise may be more sensitive for the detection of HFpEF. Although there is no formalized consensus, a provocative rise in PAOP to ≥ 20 mm Hg is likely an abnormal response., If exercise hemodynamics are obtained, thermodilution is necessary for measurement of CO unless the catheterization laboratory is capable of direct measurement of oxygen consumption. Although exercise RHC is safe, it can be challenging to complete and interpret even in the most experienced hands. Notably, protocols vary from study to study and institution to institution. At our institution, we use a semisupine cycle ergometer, but protocols also exist for an upright cycle ergometer, treadmill, or arm ergometry. The goal of exercise is to increase the heart rate to 85% of the maximal age-predicted heart rate, as is used in cardiac stress testing. Some hemodynamics, specifically the PAOP, may be difficult to obtain at peak exercise. Further, once collected, the data may be difficult to interpret because of motion artifact caused by exercise. Interpreting representative values at end-expiration is even more crucial with exercise, as respirophasic pleural pressure changes become exaggerated as tidal volumes increase.