This research study will compare two standard of care approaches for managing low sodium levels in heart failure patients with Left Ventricular Assist Device (LVAD). The study will compare the outcomes of LVAD patients with low sodium levels who take Tolvaptan to those who do not take Tolvaptan. Tolvaptan is FDA approved for use in the study population and is commonly used to treat low sodium levels in heart failure and LVAD patients. It is not known if taking Tolvaptan or not taking Tolvaptan is better at improving outcomes in newly implanted LVAD patients with low sodium levels. By doing this study, the Principal Investigator (PI) hopes to learn which is better at improving outcomes.

Inclusion Criteria:

• Hospitalized patients with American College of Cardiology (ACC) and the American Heart Association (AHA) Stage D heart failure and plan to undergo LVAD implantation
• Age greater than or equal to 18 years old

Exclusion Criteria:

• No plan for LVAD implantation
• Age less than 18 years old

The study will include patients at University of Chicago Medical Center (UCMC) being followed by the advanced heart failure group that are planned to undergo LVAD implantation.