In atherosclerosis, often called hardening of the arteries, fatty substances called lipids accumulate in the artery walls, especially those of the heart, brain, and kidneys, where they turn to plaque and cause the artery to stiffen. The circulation then becomes sluggish, and insufficient oxygen is carried to the different parts of the body. The heart disease that results causes nearly one of every three deaths in the United States. In the earlier stages of the disease the brain, sensing it is being deprived of oxygen, emits a distress signal. The heart and lungs then begin working harder to step up the brain's oxygen supply, and the increased cardiopulmonary activity often results in fragmented sleep.

Angina is the choking or suffocating pain that arises when the myocardium, the thick central muscle of the heart, is deprived experts think that sleep-disrupting anginal attacks may be triggered by the physiologic changes of the REM stage, perhaps even by the emotional content of the dreams that occur during that part of the sleep cycle.

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