In studies of sleep following acute myocardial infarction, marked disturbances have been found in patients, whether in the ICU and on the wards. These disturbances include long periods of wakefulness; poor sleep efficiency, and disruption of REM sleep. The fact that there is also a loss in circadian rhythm in these patients may indicate a widespread disruption of bodily homeostasis which, in turn, may be related to the infarct itself, to a more generalized physiological response to stress or to other factors. Sleep disruption can induce sympathetic activation and elevation of blood pressure, which may contribute to patient morbidity.