Arterial Spasms

• Partial or complete heart blockage can occur when one of your arteries spasms. The American Heart Association states these spasms can happen in arteries that are clear. The exact cause of coronary artery spasm is unknown, but the Merck Manuals report they can be brought on by cocaine or nicotine use.
  
  

Inflammation

• According to the Texas Heart Institute, researchers have found that many heart-attack victims have swollen or inflamed artery walls. These inflamed walls act as a storehouse for "vulnerable plaque." Unlike the commonly known plaque that narrows and/or fills up an open artery, vulnerable plaque spills out from within the artery walls themselves to block blood flow. The institute emphasizes that not all inflamed arteries rupture. Other health conditions, such as high blood pressure, must be present.
  
  

Expert Insight

• The American Heart Association reports that statin therapy (drug treatment commonly used to lower high cholesterol) may reduce the need for artery-opening procedures in people with normal or even low cholesterol levels if those people also have elevated levels of C-reactive protein in their blood. C-reactive protein is a marker of how much inflammation is in the body, including the arteries.
  
  

Hypertension

• High blood pressure, hypertension, is the condition in which blood chronically flows through the arteries too forcefully. This constantly high pressure can cause artery walls to stretch and weaken, making them vulnerable to blood-vessel ruptures that can cause blockages due to blood clots and the vulnerable plaque associated with inflammation.
  
  

Bundle Branch Block

• Bundles of cardiac fibers in the right and left ventricles of the heart are responsible for carrying the electrical signals that tell your heart when to beat. Sometimes these bundles become damaged to the point that the electrical impulse can't pass through. This condition, called bundle branch block, makes it harder for your heart to pump blood efficiently.
  
  According to the Mayo Clinic, a bundle branch block can be caused by several underlying conditions, including previous heart attack, diseased heart muscle and hypertension.
  
  

Smoking

• The Journal of the American Medical Association reports that smoking narrows the arteries in the heart, leaving you vulnerable to hypertension and its complications, including coronary blockage from blood clots. Additionally, even if your cholesterol is within the normal range now, smoking can eventually decrease your good cholesterol (HDL) and leave your arteries vulnerable to the accumulation of plaque.