the more common. Left-sided failure The left side of the heart takes oxygen-rich blood from the lungs and pumps it to the rest of the circulatory system in the body, except for the pulmonary circulation). Failure of the left side of the heart causes blood to back up into the lungs, causing breathing difficulties and fatigue due to an insufficient supply of oxygenated blood. Common respiratory signs include increased respitatory rate and labored breathing (nonspecific signs of shortness of breath). Rales or crackles heard initially in the lung bases and when severe in all lung fields indicate the development of pulmonary edema (fluid in the alveoli). Cyanosis, indicates deficiency of oxygen in the blood, is a late sign of extremely severe pulmonary edema. Other signs of left ventricular failure include a laterally displaced apex beat (which occurs when the heart is enlarged) and a gallop rhythm (additional heart sounds), which may be heard as a sign of increased blood flow or increased intracardiac pressure. Heart murmurs may indicate the presence of valvular heart disease, either as a cause (e.g., aortic stenosis) or as a consequence (e.g., mitral regurgitation) of heart failure. Reverse insufficiency of the left ventricle causes congestion in the blood vessels of the lungs, so that symptoms are predominantly respiratory. Reverse insufficiency can be divided into the failure of the left atrium, the left ventricle, or both within the left circuit. Patients will experience shortness of breath (dyspnea) on exertion and, in severe cases, dyspnea at rest. Increasing breathlessness while lying down, called orthopnea, also occurs. It can be measured by the number of pillows required to lie comfortably, with extreme cases of orthopnea forcing the patient to sleep sitting up. Another symptom of heart failure is paroxysmal nocturnal dyspnea: a sudden nocturnal attack of severe shortness of breath, usually occurring several hours after falling asleep. There may be "cardiac asthma" or wheezing. Impaired left ventricular forward function can lead to symptoms of poor systemic perfusion such as dizziness, confusion, and cool extremities at rest. Right-sided failure Right-sided heart failure is often caused by pulmonary heart disease (cor pulmonale), which is typically caused by issues with pulmonary circulation such as pulmonary hypertension or pulmonic stenosis. Physical examination may reveal pitting peripheral edema, ascites, liver enlargement, and spleen enlargement. Jugular venous pressure is frequently assessed as a marker of fluid status, which can be accentuated by testing hepatojugular reflux.