Heart failure is a complex clinical syndrome characterized by impaired myocardial performance and progressive maladaptive neurohormonal adaptation. It can be systolic or diastolic in nature. Common causes include ischemia, cardiomyopathy, hypertension, and valvular disorders. Symptoms include dyspnea, orthopnea, fatigue, and ankle swelling. Diagnostic evaluation involves ECG, echocardiogram, blood tests, and cardiac catheterization. Management depends on whether the heart failure is acute or chronic, and involves treatments like oxygen, vasodilators, diuretics, beta blockers, ACE inhibitors, and device therapies like ICDs or CRT. Lifestyle changes like exercise and diet are also important.