The smaller branches of these arteries usually have con-
nections (anastomoses) between vessels that provide alter-
nate pathways for blood, called collateral circulation. These
detours in circulation may supply oxygen and nutrients to
the myocardium when a coronary artery is blocked.
An angiogram (radiograph) of the coronary arteries
is a diagnostic procedure used to examine speciF
c blood vessels.
Right coronary artery
Left coronary artery
walls of right
atrium and right
walls of left
atrium and left
of blood through the
Branches of the
drain blood that has
passed through the capillaries of the myocardium. Their
paths roughly parallel those of the coronary arteries. As F g-
shows, these veins join the
enlarged vein on the posterior surface of the heart in the
atrioventricular sulcus. The coronary sinus empties into the
summarizes the path of blood that
supplies the tissues of the heart.
In most body parts, blood ﬂ ow in arteries peaks during
ventricular contraction. However, blood ﬂ
ow in the vessels
of the myocardium is poorest during ventricular contrac-
tion. This is because the muscle F
bers of the myocardium
compress nearby vessels as they contract, interfering with
blood flow. Also, the openings into the coronary arteries
are partially blocked as the ﬂ
aps of the aortic valve open.
Conversely, during ventricular relaxation, the myocardial
vessels are no longer compressed, and the aortic valve does
not block the oriF
ces of the coronary arteries. This increases
ow into the myocardium.
A thrombus or embolus that blocks or narrows a coronary artery
branch deprives myocardial cells of oxygen, producing ischemia and
The pain usually occurs during physical activ-
ity, when oxygen requirements exceed supply. Pain lessens with rest.
Emotional stress may also trigger angina pectoris.
Angina pectoris may cause a heavy pressure, tightening, or
squeezing sensation in the chest. The pain is usually felt behind the
sternum or in the anterior portion of the upper thorax, but may radi-
ate to the neck, jaw, throat, shoulder, upper limb, back, or upper
abdomen. Other symptoms include profuse perspiration (diaphore-
culty breathing (dyspnea), nausea, or vomiting.
A blood clot completely obstructing a coronary artery or one
of its branches (coronary thrombosis) kills part of the heart. This is a
(MI), more commonly known as a heart attack.