This study looks at whether a thyroid hormone called triiodothyronine (T3) can help people with ischemic heart failure, which is a type of heart disease where the heart doesn't pump blood well. In the first phase of the study, participants may either receive T3 or not, and those who do will stay in a research center for 5 days for treatment and monitoring. Everyone will have 4 follow-up visits over the next year. In the second phase, everyone will receive T3 treatment. The goal is to see if T3 can improve heart function without causing bad side effects. If T3 treatment works, it could become a new way to help people with heart failure.

• Participants must be 18-80 years old with specific heart conditions.
• The study involves a short stay in a clinic and follow-up visits.
• Those who qualify may receive treatment and help advance heart disease research.