The goal of this observational study is to learn about heart function and high lung blood pressure in patients with heart failure. The main question[s] it aims to answer are whether we can improve the ability to predict patients who will have complications after they receive treatment including heart transplant and left ventricular assist devices.

Prospective cohort study of patients with heart failure with reduced ejection fraction that are referred for diagnostic right heart catheterization as part of their evaluation for candidacy for advanced heart failure therapies.

Inclusion Criteria:

• Adults age 18 years or older
• Heart failure with reduced ejection fraction (<40%)
• referred for RHC at our centre for evaluation of candidacy for advanced HF therapies.

Exclusion Criteria:

Severe valvular or complex congenital heart disease Short-term mechanical circulatory support for progressive cardiogenic shock (e.g. extracorporeal membrane oxygenation) Acute coronary syndrome or revascularization occurred within 7 days prior to the RHC.

Pregnant or breast-feeding Known hypersensitivity to sodium nitroprusside Advanced liver dysfunction Reduced capacity or inability to provide informed consent

Patients assessed in the advanced heart failure program for heart transplant candidacy at the University of Toronto referred for right heart catheterization.

Agreements to share participant data can be requested after study completion and publication.