Levosimendan is being studied to check if it helps people with a type of heart problem called PH-HFpEF (pulmonary hypertension with heart failure and preserved ejection fraction). This study will see if taking levosimendan can help people walk farther in a 6-minute walking test. Participants are chosen randomly to receive either the medicine or a placebo (a pill with no medicine) for 12 weeks without knowing which one they are taking. After 12 weeks, they can choose to stay in the study for up to 92 more weeks. Before starting, a screening period of up to 30 days checks if they can join the study.

• The study lasts 12 weeks and includes a possible extension of 92 more weeks.
• 230 participants are needed, and they will be randomly assigned the treatment.
• Participants will have several health checks before and during the study.

To join, participants must be 18 to 85 years old and have PH-HFpEF. They should not have certain other heart or lung problems. It's important to discuss with a doctor before joining to understand the possible benefits and risks.