Participants in this study will undergo a series of adjustments to their pacemaker that will be made while they are undergoing routine, clinically indicated right heart catheterization in the outpatient setting after their left ventricular assist device (LVAD) surgery. Patients will undergo the study procedures while in the catheterization lab under controlled conditions. The study protocol involves increasing the rate that the pacemaker paces at. While the pacemaker is set to pace at different, increasing heart rates, pressures will be measured in the different chambers of the heart utilizing a special type of intravenous (IV) line called a pulmonary artery catheter. Several small blood samples will also be drawn from this venous catheter in order to measure oxygen levels in the blood. It will take approximately 30 minutes to perform the study, and when it is completed, the pacemaker will be returned to its original settings.

The purpose of the study is to evaluate the safety and how well the medication sotatercept works versus placebo in treating Heart Failure with a Preserved Ejection Fraction. The study will also look at information obtained from the tests performed as part of the study to see if subjects have improvement in symptoms of heart failure. Participation in this study will last approximately 26 months. During the study period subjects will be asked to attend regular study visits with the research coordinator. These visits will include such activities as blood tests, questionnaires, physical evaluation by a study doctor, a right heart catheterization with exercise, echocardiogram, and 6 minute hall walks. There will be 35 visits as part of participation in this clinical trial.

Participants will be randomized to either the treatment group (and receive the medication) or the control group (and not receive the medication). Subjects will have a 66:33 chance of receiving the study medication during their participation in the trial. The treatment assignment is determined by randomization, where a computer selects at random which treatment group you will be in (like drawing straws). Neither the subject, nor the blinded personnel will know which group subjects are in. Neither the subject nor the study doctor will decide what group subjects are assigned.

The purpose of the study is to evaluate the safety and how well the medication levosimenden works versus placebo in treating Pulmonary Hypertension and Heart Failure with a Preserved Ejection Fraction measured by a 6 minute walk. This is a condition where the lower left chamber (left ventricle) of the heart is not able to fill properly with blood during the filling phase and the amount of blood pumped out to the body is below normal. The study will also look at information obtained from the tests performed as part of the study to see if subjects have improvement in symptoms of heart failure. Levosimendan is a drug that has been FDA-approved for intravenous (IV) delivery to your body. This study aims to determine if the tablet form of the drug is as effective as the IV route. Tablets are much more attainable for patients to manage their heart failure from home, rather than going to an infusion clinic for treatments. Participation in this study will last approximately 12 weeks with the option to continue to the stage 2 phase of the study. If the stage 2 phase is selected as well, participation will last approximately 26 months or a little over 2 years. These visits will include such activities as blood tests, questionnaires, physical evaluation by a study doctor, echocardiogram, and 6 minute hall walks.

Participants will be randomized to either the treatment group (and receive the medication) or the control group (receive an inactive medication). Subjects will have a 50:50 chance of receiving the study medication during their participation in the trial. The treatment assignment is determined by randomization, where a computer selects at random which treatment group you will be in (like drawing straws). Neither the subject, nor the blinded personnel will know which group subjects are in. Neither the subject nor the study doctor will decide what group subjects are assigned.