The concept of homeostasis in biology postulates that there is constancy of the intern milieu. Thus is assumed the risk and exacerbation of disease are invariable and independent of the time of day, day of month, and month of year as are the responses of patients to diagnostic tests and medications. Findings from the field of chronobiology, the study of biological rhythms, challenge the concept of homeostasis and the many assumptions and procedures of clinical medicine based on it. It is now recognized that human functions have daily, weekly, monthly and yearly biological rhythms. Plants, animals, and insects also have chronobiological rhythms. Circadian patterns have been observed for variety of cardiovascular disorders, including cardiac arrhythmias, sudden cardiac death, cerebrovascular events, episodes of stable angina, unstable angina and acute myocardial infarction. The morning predominance of these events has been well documented in a number of large population studies. It is now recognized that circadian and other rhythms of the gastrointestinal tract and vital organs are capable of significantly affecting the pharmacokinetics and dynamics of cardiovascular and other medications. This means that the effects of therapeutic interventions administered in identical doses in the morning versus the evening may not be equivalent. The prevention and treatment of cardiovascular disease must take into account chronobiological factors.

Keywords: Cardiovascular Diseases /diagnosis/; Chronobiology Phenomena; Chronotherapy; Circadian Rhythm; Humans