Heart muscle diseases, also known as cardiomyopathies, are a group of conditions that primarily affect the heart's muscle tissue (the myocardium). These diseases impair the heart's ability to pump blood effectively to the rest of the body. The heart muscle can become thickened, stretched, or stiff, leading to a weakened heart and various complications such as heart failure, irregular heartbeats (arrhythmias), blood clots, and even sudden cardiac arrest. Cardiomyopathies can be caused by a variety of factors, including genetic mutations, high blood pressure, infections, alcohol or drug abuse, and other underlying medical conditions. In some cases, the cause of cardiomyopathy remains unknown (idiopathic). The symptoms can vary widely depending on the type and severity of the cardiomyopathy, but common signs include shortness of breath, fatigue, chest pain, swelling in the legs and ankles, and palpitations. Diagnosis often involves a combination of physical examination, medical history review, and various cardiac tests such as electrocardiograms (ECGs), echocardiograms, cardiac magnetic resonance imaging (MRI), and sometimes cardiac catheterization and biopsy. Treatment strategies focus on managing symptoms, slowing the progression of the disease, and preventing complications, and may include medications, lifestyle modifications, implanted devices, or in severe cases, heart transplantation.