Society of Cardiology defines the diagnosis of heart failure as symptoms and signs consistent with heart failure in combination with "objective evidence of cardiac structural or functional abnormalities". This definition is consistent with an international 2021 report termed "Universal Definition of Heart Failure". Score-based algorithms have been developed to help in the diagnosis of HFpEF, which can be challenging for physicians to diagnose. The AHA/ACC/HFSA defines heart failure as symptoms and signs consistent with heart failure in combination with shown "structural and functional alterations of the heart as the underlying cause for the clinical presentation", for HFmrEF and HFpEF specifically requiring "evidence of spontaneous or provokable increased left ventricle filling pressures". Algorithms The European Society of Cardiology has developed a diagnostic algorithm for HFpEF, named HFA-PEFF. HFA-PEFF considers symptoms and signs, typical clinical demographics (obesity, hypertension, diabetes, elderly, atrial fibrillation), and diagnostic laboratory tests, ECG, and echocardiography. Classification One historical method of categorizing heart failure is by the side of the heart involved (left heart failure versus right heart failure). Right heart failure was thought to compromise blood flow to the lungs compared to left heart failure compromising blood flow to the aorta and consequently to the brain and the remainder of the body's systemic circulation. However, mixed presentations are common and left heart failure is a common cause of right heart failure. More accurate classification of heart failure type is made by measuring ejection fraction, or the proportion of blood pumped out of the heart during a single contraction. Ejection fraction is given as a percentage with the normal range being between 50 and 75%. The types are: Heart failure with reduced ejection fraction (HFrEF): Synonyms no longer recommended are "heart failure due to left ventricular systolic dysfunction" and "systolic heart failure". HFrEF is associated with an ejection fraction less than 40%. Heart failure with mildly reduced ejection fraction (HFmrEF), previously called "heart failure with mid-range ejection fraction", is defined by an ejection fraction of 41–49%. Heart failure with preserved ejection fraction (HFpEF): Synonyms no longer recommended include "diastolic heart failure" and "heart failure with normal ejection fraction." HFpEF occurs when the left ventricle contracts normally during systole, but the ventricle is stiff and does not relax normally during diastole, which impairs filling. Heart failure may also be classified as acute or chronic. Chronic heart failure is a long-term condition, usually kept stable by the treatment of symptoms. Acute