This study explores if a thyroid hormone, Triiodothyronine (T3), is safe and can help people with ischemic heart failure feel better. Heart failure means the heart isn't pumping blood as well as it should. The research is split into two parts:

• In the first phase, participants have a 50% chance to receive T3. Those who do will stay in a hospital for 5 days for treatment and check-ups. Everyone will have 4 follow-up visits in a year.
• If you don't get T3 in phase one, you can join phase two, where everyone receives T3 treatment.

The goal is to see if T3 can improve heart function without causing serious problems. If successful, this could lead to new treatments for heart failure.

• Study lasts up to one year with 5 main visits.
• Some participants will stay 5 days in a hospital for treatment.
• No major side effects like arrhythmias observed in preliminary studies.