ATR may refer to:
Atrial fibrillation (AF or A-fib) is an abnormal heart rhythm characterized by rapid and irregular beating.
Atropine is a medication used to treat certain types of nerve agent and pesticide poisonings, some types of slow heart rate, and to decrease saliva production during surgery.
The ATR 72 is a twin-engine turboprop short-haul regional airliner manufactured by the French-Italian aircraft manufacturer ATR.
Atrial septal defect (ASD) is a congenital heart defect in which blood flows between the atria (upper chambers) of the heart.
Atropa belladonna, commonly known as belladonna or deadly nightshade, is a perennial herbaceous plant (rhizomatous hemicryptophyte) in the Nightshade family (which includes tomatoes, potatoes, eggplant, etc.) Solanaceae, native to Europe, North Africa, and Western Asia.
The ATR 42 is a twin-turboprop, short-haul regional airliner built in France and Italy by ATR (Aerei da Trasporto Regionale or Avions de transport régional).
In the period from 1885 to 1908, a number of well-documented atrocities were perpetrated in the Congo Free State (today the Democratic Republic of the Congo) which, at the time, was a colony under the personal rule of King Leopold II of Belgium.
Atrial natriuretic peptide (ANP), also called atrial natriuretic factor (ANF), atrial natriuretic hormone (ANH), cardionatrine, cardiodilatin (CDD), or atriopeptin, is a powerful vasodilator, and a protein (polypeptide) hormone secreted by heart muscle cells.
The atrium (plural: atria) is a blood collection chamber of the heart. It was previously called the auricle, and that term is still used to describe this chamber in, for example, the Mollusca, but in humans that name is now used for an appendage of the atrium.