This study tests a medicine called levosimendan to help people with a heart condition called PH-HFpEF (stands for Pulmonary Hypertension with Heart Failure and preserved Ejection Fraction). The main goal is to see if levosimendan helps people walk further in 6 minutes after taking it for 12 weeks. The study is done in a way where neither the doctors nor the patients know who gets the real medicine or a fake one (called a placebo). About 152 people will take part, aged between 18 and 85 years. Participants will first go through a check-up period of up to 30 days. After that, they will be part of a 12-week treatment phase. They may continue for another 92 weeks if they choose. Only people who meet certain health requirements can join. Some who have certain heart or lung diseases, or recent surgeries, cannot take part.

• Study length: Up to 12 weeks, with an optional additional 92 weeks.
• Participants: 152 people, aged 18-85.
• Participants must meet specific health conditions to join.