Inclusion Criteria:

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

Exclusion Criteria:

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