Not only are findings from invasive studies in patients with congestive heart failure important for diagnosis, they may also be crucial in deciding on appropriate treatment and predicting prognosis. Hemodynamic evaluation may be useful for tailoring medical therapy, determining the need for mechanical support, predicting survival, deciding when valve surgery is needed, locating intracardiac shunts precisely, assessing the severity of pulmonary hypertension before cardiac transplantation, or diagnosing unexplained dyspnea. Contrast angiography can be used to evaluate systolic function if information from noninvasive studies is inadequate. Coronary arteriography can help determine the severity and extent of coronary artery disease and is needed if revascularization is being contemplated. Endomyocardial biopsy can be used to identify the cause of cardiomyopathy.