loosely refers to the hearts electrical axis when this is directed at approximately 0°. As a cardiac electrical position, recognized in the electrocardiogram when the QRS complex in lead aVL resembles V6 whereas that in aVF is small algebraically or absolutely.
an electric "position" of the heart that lies between the horizontal and intermediate positions when the QRS axis is 0 degrees.
sem·i·hor·i·zon·tal heart(sem'ē-hōr'i-zon'tăl hahrt)
Refers to the heart's electrical axis when this is directed at approximately 0 degrees.