Volunteers are being asked to participate in a clinical research study to find out if the drug mavacamten is safe and effective in treating elevated biomarker levels that occur in patients who have Heart Failure with Preserved Ejection Fraction (HFpEF). HFpEF is a syndrome that leads to stiffening in the left bottom chamber of the heart. This stiffening makes it difficult for the chamber to relax enough to fill up with blood, leading to increased pressure inside of the heart. MyoKardia is doing this research to find out if the new medication called mavacamten will work and be safe for the treatment of heart failure patients with the elevated levels the biomarkers NT-proBNP (a marker of wall stress inside the heart) and/or cardiac troponin (a marker of heart muscle injury). Biomarkers are biological molecules found in bodily fluids that can indicate abnormal conditions within the body. The study is planned to go on for about 2 years and include 35 patients from about 30 different study sites.

The purpose of the study is to evaluate the safety and how well the V-Wave Interatrial Shunt works. The study will also look at information obtained from the tests performed to see if subjects have improvement in symptoms of heart failure. Participation in this study will last approximately 1 year to up to 7 years depending on randomization group. 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, echocardiogram, and 6 minute hall walks. There will be a minimum of 10 or up to 15 planned research clinic visits. Subjects will have 1 overnight hospital stay for the study related RHC and research procedure. Due to the COVID-19 pandemic, study participants may be discharged the same day when necessary. Each participant will receive a phone call between all study visits.

Subjects will have a 50:50 chance of receiving the Shunt during the randomization procedure (like the flip of a coin). Neither the subject, nor the blinded study doctor or blinded study coordinator will know which group subjects are in. Participants will be randomized to either the treatment group (and receive the Shunt) or the control group (and not receive the shunt). Neither the subject nor the study doctor will decide what group subjects are assigned.