The study will be an open label one and will include 30 patients who underwent ischemic stroke 3 month to 3 years prior to the study. All patients will undergone a baseline brain SPECT perfusion study. 15 patients will take one dose of 20 mg cialis, and will have a second brain SPECT 24 hours after cialis administration. 15 other patients (age and risk factor matched) will be prescribed 5 mg of cialis once daily for 7 days, and a second SPECT study will be performed 24 hours after the last dose.

Inclusion Criteria:

• Male and female patients in the age range of 35-75 years.

Exclusion Criteria:

1. known allergic reaction to TF
2. Medical contraindication to use TF
3. Hemorrhagic stroke including intracerebral hemorrhage and subarachnoid hemorrhage
4. Acute stroke or cardiac ischemic event up to 3 month prior to study.
5. Other neurological brain diseases including degenerative diseases, multiple sclerosis, brain tumors, post severe brain injury (TBI) and migraine headache.
6. Sensory aphasia.
7. Cognitive impairment with disability to sign a consent form.Patients' Assessment

Male and female patients in the age range of 35-75 years.