The investigators will measure endothelial glycocalyx, aortic elastic properties, oxidative stress, and their association with left ventricular (LV) and left atrial (LA) function in ESUS, cardioembolic, atherosclerotic, lacunar strokes and age- and sex-adjusted healthy individuals.

Investigators plan to include male and female patients, aged 18 to 75 years old admitted and hospitalized in the 2nd Neurology Department of Attikon University Hospital for Acute Ischemic Stroke, based on the Trial of Org 10172 in Acute Stroke Treatment TOAST classification. The TOAST classification consists of five categories: 1) large artery atherosclerosis (atherothrombotic), 2) cardioembolic, 3) small artery occlusion (lacunar), 4) stroke of undetermined etiology (ESUS).

In participants (patients and controls) the investigators plan to measure and compare: a) perfused boundary region (PBR) of the sublingual arterial microvessels (range 5-25 micrometers), a marker inversely related with glycocalyx thickness, b) pulse wave velocity (PWV), central systolic blood pressure (cSBP) and augmentation index (AIx), c) LV Global Longitudinal strain (GLS), d) LA volume and strain using speckle-tracking strain imaging, e) Malondialdehyde (MDA), as an oxidative stress marker.

Inclusion Criteria:

The investigators plan to include participants with Acute Ischemic Stroke, based on the TOAST classification : 1) large artery atherosclerosis (atherothrombotic), 2) cardioembolic, 3) small artery occlusion (lacunar), 4) stroke of undetermined etiology (ESUS). According to the TOAST classification, diagnoses are based on clinical presentation and on data collected by exams such as brain imaging (CT/MRI), cardiac imaging (echocardiography) and laboratory tests for the prothrombotic state. The diagnosis of Embolic Stroke of Undetermined Source (ESUS) was established based on the criteria defined by the Cryptogenic Stroke/ESUS International Working Group.

Exclusion Criteria

1. presence of acute haemorrhagic stroke,
2. the presence of stroke of other determined etiology,
3. the history of previous Ischemic stroke and/or Myocardial Infarction (MI),
4. hypercoagulable state,
5. active malignancy
6. severe chronic kidney disease (eGFR<30 ml/minute). These exclusion criteria are applied to both patients and control subjects.

The study population will consist of 172 consecutive patients with Ischemic stroke of undetermined source (ESUS) that fulfill inclusion criteria and 43 healthy volunteers of similar age and sex (control group)