Heart failure (HF), also known as congestive heart failure (CHF), is when the heart is unable to pump sufficiently to maintain blood flow to meet the body's needs. Signs and symptoms of heart failure commonly include shortness of breath, excessive tiredness, and leg swelling. The shortness of breath is usually worse with exercise, while lying down, and may wake the person at night. A limited ability to exercise is also a common feature. Chest pain, including angina, does not typically occur due to heart failure. Common causes of heart failure include coronary artery disease including a previous myocardial infarction (heart attack), high blood pressure, atrial fibrillation, valvular heart disease, excess alcohol use, infection, and cardiomyopathy of an unknown cause. These cause heart failure by changing either the structure or the functioning of the heart. The two types of heart failure – heart failure with reduced ejection fraction (HFrEF), and heart failure with preserved ejection fraction (HFpEF) – are based on whether the ability of the left ventricle to contract is affected, or the heart's ability to relax. The severity of disease is graded by the severity of symptoms with exercise. Heart failure is not the same as myocardial infarction (in which part of the heart muscle dies) or cardiac arrest (in which blood flow stops altogether). Other diseases that may have symptoms similar to heart failure include obesity, kidney failure, liver problems, anemia, and thyroid disease. Heart failure is diagnosed based on the history of the symptoms and a physical examination, with confirmation by echocardiography. Blood tests, electrocardiography, and chest radiography may be useful to determine the underlying cause. Treatment depends on the severity and cause of the disease. In people with chronic stable mild heart failure, treatment commonly consists of lifestyle modifications such as stopping smoking, physical exercise, and dietary changes, as well as medications. In those with heart failure due to left ventricular dysfunction, angiotensin converting enzyme inhibitors, angiotensin receptor blockers, or valsartan/sacubitril along with beta blockers are recommended. For those with severe disease, aldosterone antagonists, or hydralazine with a nitrate may be used. Diuretics are useful for preventing fluid retention and the resulting shortness of breath. Sometimes, depending on the cause, an implanted device such as a pacemaker or an implantable cardiac defibrillator (ICD) may be recommended. In some moderate or severe cases, cardiac resynchronization therapy (CRT) or cardiac contractility modulation may be of benefit. A ventricular assist device (for the left, right, or both ventricles), or occasionally a heart transplant may be recommended in those with severe disease that persists despite all other measures. Heart failure is a common, costly, and potentially fatal condition. In 2015, it affected about 40 million people globally. Overall around 2% of adults have heart failure and in those over the age of 65, this increases to 6–10%. Rates are predicted to increase. The risk of death is about 35% the first year after diagnosis; while by the second year the risk of death is less than 10% for those who remain alive. This degree of risk of death is similar to some cancers. In the United Kingdom, the disease is the reason for 5% of emergency hospital admissions. Heart failure has been known since ancient times, with the Ebers papyrus commenting on it around 1550 BCE. Heart failure symptoms are traditionally and somewhat arbitrarily divided into 'left' and 'right' sided, recognizing that the left and right ventricles of the heart supply different portions of the circulation. However, heart failure is not exclusively backward failure (in the part of the circulation which drains to the ventricle). There are several other exceptions to a simple left-right division of heart failure symptoms. Additionally, the most common cause of right-sided heart failure is left-sided heart failure. The result is that people commonly present with both sets of signs and symptoms. The left side of the heart is responsible for receiving oxygen-rich blood from the lungs and pumping it forward to the systemic circulation (the rest of the body except for the pulmonary circulation). Failure of the left side of the heart causes blood to back up (be congested) into the lungs, causing respiratory symptoms as well as fatigue due to insufficient supply of oxygenated blood. Common respiratory signs are increased rate of breathing and increased work of breathing (non-specific signs of respiratory distress). Rales or crackles, heard initially in the lung bases, and when severe, throughout the lung fields suggest the development of pulmonary edema (fluid in the alveoli). Cyanosis which suggests severe low blood oxygen, is a late sign of extremely severe pulmonary edema. Additional signs indicating left ventricular failure include a laterally displaced apex beat (which occurs if the heart is enlarged) and a gallop rhythm (additional heart sounds) may be heard as a marker of increased blood flow or increased intra-cardiac pressure. Heart murmurs may indicate the presence of valvular heart disease, either as a cause (e.g. aortic stenosis) or as a result (e.g. mitral regurgitation) of the heart failure.