A coronary artery spasm is a sudden, temporary contraction of muscle fibers within the walls of the coronary artery. The coronary arteries supply oxygenated blood to the muscle of the heart (see fig. 1). Coronary artery spasm occurs in a small, localized area of the vessel and it blocks the passage of blood through the artery (see fig. 2).

Figure 1: Heart with coronary arteries.

Figure 2: Coronary artery spasm.