The "LAD", or left anterior descending artery (or anterior interventricular branch of the left coronary artery, or anterior descending branch) is an artery of the heart.
It passes at first behind the pulmonary artery and then comes forward between that vessel and the left auricula to reach the anterior interventricular sulcus, along which it descends to the incisura apicis cordis.
In 78% of cases, it reaches the apex of the heart.
It supplies the anterolateral myocardium, apex, and interventricular septum. The LAD typically supplies 45-55% of the left ventricle (LV).
The LAD gives off two types of branches: septals and diagonals.
- Septals originate from the LAD at 90 degrees to the surface of the heart, perforating and supplying the anterior 2/3rds of the interventricular septum.
- Diagonals run along the surface of the heart and supply the lateral wall of the left ventricle and the anterolateral papillary muscle.
Tight, critical stenosis (95%) of the proximal LAD in a patient with Wellens' Warning
"The Widowmaker" 
Because the LAD provides much of the bloodflow for the left ventricle, which in turn provides much of the propulsive force for ejecting oxygenated blood to systemic circulation via the aorta, blockage of this artery is particularly associated with mortality. In the medical community ischemic heart attacks associated with this blood vessel are colloquially called "the Widowmaker."
Additional images 
Coronary arteries (labeled in red text) and other major landmarks (in blue text). Left anterior descending (or interventricular) artery
is labeled at right.
The arch of the aorta, and its branches.
Human heart with coronary arteries
Heart coronary territories
External links 
This article incorporates text from a public domain edition of Gray's Anatomy.