PH-HFpEF patients will receive open-label doses of levosimendan and be periodically evaluated for safety in extended use.

This study will enroll PH-HFpEF patients that have completed a controlled levosimendan study. These patients will receive open-label doses of levosimendan and be periodically evaluated for safety in extended use.

Inclusion Criteria:

1. Provide a personally signed and dated informed consent document prior to initiation of any study-related procedures that are not considered standard of care.
2. Completed double-blind therapy in a PH-HFpEF clinical study sponsored by Tenax Therapeutics, Inc.
3. May, in the opinion of the Investigator, benefit from continued levosimendan treatment.
4. Female patients of childbearing potential must agree to use a highly effective method of contraception.
5. Willingness and ability to comply with scheduled visits, treatment plan, laboratory tests and other study procedures.

Exclusion Criteria:

1. Discontinued treatment in the parent study for any reason other than study completion or Sponsor termination of the study.
2. Pregnant or breastfeeding women.
3. Local access to commercially available levosimendan
4. Inability to comply with planned study procedures
5. Patients with scheduled lung or heart transplant or cardiac surgery
6. Dialysis developed since enrollment in parent study (either hemodialysis, peritoneal dialysis, continuous venovenous hemofiltration, or ultrafiltration)
7. Estimated glomerular filtration rate (eGFR) <30 mL/min/1.73m2
8. Liver dysfunction with Child Pugh Class B or C (see Attachment 2)
9. Evidence of systemic bacterial, systemic fungal, or viral infection refractory to treatment
10. Weight >150kg
11. Systolic blood pressure (SBP) cannot be managed to ensure SBP >100 mmHg at initiation of study drug
12. Heart rate >100 bpm with study drug, persistent for at least 10 minutes at screening.
13. Hemoglobin < 80 g/L
14. Serum potassium < 3.0 mmol/L or > 5.5 mmol/L at baseline that is unresponsive to management