Can an echocardiogram show if there is restricted blood supply to the heart?

Echo: The echo will only show restricted blood flow if you stress the heart with exercise (treadmill) while performing it, a so-called stress echo.

If you mean: Restricted blood supply by coronary disease causing ischemia, a part of the heart can show hypokinesia/akinesia. An abnormal wall motion abnormality that correlate with a specific coronary artery. Also can show an abnormality call restrictive cardiomiopathy that is a non-ischemic type of cardiomiopathy that affect the structure of the heart causing restriction of blood supply if severe.