It is recognized that endothelial dysfunction is a major factor contributing to the atherogenic process. Abnormal function of the endothelium is detectable prior to obvious intimal lesions in patients with risk factors for atherosclerosis. Endothelial dysfunction is a systemic disorder and a key variable in the pathogenesis of atherosclerosis and its complications. Measurement of peripheral vasodilator response with fingertip peripheral arterial tonometry (PAT) technology (EndoPAT; Itamar Medical, Caesarea, Israel) is emerging as a useful method for assessing vascular function. EndoPAT may be a potential valid test increasing the accuracy, sensitivity and specificity for detection of subjects to chest pain unit (CPU) with chest pain but no obvious coronary artery disease (CAD). This is a relatively fast non-invasive bedside test, relatively low-cost and has no side effects. Therefore, the primary objective of the study is to test the hypothesis that abnormal endothelial function as assessed by EndoPAT testing will increase the prediction of the short (in-hospital) and long-term (1-year) outcome of patients presenting to the chest pain unit.

All subjects admitted to the CPU with low to moderate probability for CAD and negative troponin, will undergo the following tests upon arrival following clinical evaluation and their consenting to the study: resting ECG, EndoPAT testing and then after stress nuclear imaging or stress echocardiography. Except for EndoPAT testing, all other tests will be conducted according to the routine CPU protocol.

The results of the EndoPAT will be blinded to the treating physician until the end of the study and all patients will be managed according to the current CPU protocol, including 24-h Holter monitoring, repeat resting ECG and exercise tests (nuclear SPECT imaging or stress echocardiography, whichever is available) in addition to repeat clinical and troponin tests evaluations.

All clinical data of the recruited subjects the will be recorded and evaluated after completion of the study.

Long-term clinical follow-up All patients will be followed by telephone contact after 6 and 12 months for combined major adverse cardiovascular end-points (MACE) which include all-cause mortality, non-fatal myocardial infarction, hospitalization for heart failure or angina pectoris, stroke, coronary artery bypass grafting and percutaneous coronary interventions, by physicians who will be blinded to the patients' baseline clinical status and endothelial function (assessed by EndoPAT) results. All MACE will be validated by review of medical records by senior cardiologists blinded to the endothelial function results. In addition, on-line access to this information will facilitate verification and safe documentation of all events. In addition, written medical records will be reviewed by cardiologists in the event of any death, hospitalization and/or angina pectoris.

At the end of the study the cost effectiveness on prediction of short (in-hospital) and long (6 months, and 1 year) of EndoPAT will be assessed and will be compared to the stress tests (nuclear imaging and/or echocardiography).

Inclusion Criteria:

• All subjects admitted to the CPU with low to moderate probability for CAD and negative troponin.

Exclusion Criteria:

• Subjects with chest pain and positive troponin.

All subjects admitted to the CPU with low to moderate probability for CAD and negative troponin, will undergo the following tests upon arrival following clinical evaluation and their consenting to the study: resting ECG, EndoPAT testing and then after stress nuclear imaging or stress echocardiography. Except for EndoPAT testing, all other tests were conducted according to the routine CPU protocol.