Clinical Study of Endocardial Myocardial Biopsy

This study is collecting heart tissue samples through a procedure called endocardial myocardial biopsy — a small tissue sample taken from inside the heart using a catheter — to better understand the causes of various unexplained heart conditions like myocarditis, cardiomyopathy, and heart tumors. **You may be eligible if...** - You are between 18 and 80 years old and are already scheduled to receive an endocardial biopsy at the study hospital - You have an unexplained heart condition such as myocarditis, cardiomyopathy, heart failure of unknown cause, or a cardiac tumor - You can understand the study and cooperate with researchers **You may NOT be eligible if...** - You are unwilling or unable to sign an informed consent form or participate in follow-up visits Talk to your doctor to see if this trial is right for you.