| ATR | the normal cardiac rhythm when the heart is controlled by the atrioventricular node |
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| ATR | a node of specialized heart muscle located in the septal wall of the right atrium |
| ATR | a bundle of modified heart muscle that transmits the cardiac impulse from the atrioventricular node to the ventricles causing them to contract |
| ATR | either of two heart valves through which blood flows from the atria to the ventricles |
| ATR | (nautical) of an anchor |
| ATR | orach |
| ATR | Asiatic plant resembling spinach often used as a potherb |
| ATR | handsome low saltbush of arid southwestern United States and Mexico having blue-green prickly-edged leaves often used for Christmas decoration |
| ATR | spiny shrub with silvery-scurfy foliage of alkaline plains of southwestern United States and Mexico |
| ATR | Eurasian aromatic oak-leaved goosefoot with many yellow-green flowers |
| ATR | the central area in a building |
| ATR | any chamber that is connected to other chambers or passageways (especially one of the two upper chambers of the heart) |