I had a large saddle pulmonary embolism 3 months ago & still breathless dr sendin me for a myocardial perfusion scan will this show if clot has gone ?

No : He's looking to see if your heart is working right or not and that might be the cause of your shortness of breath.

Not necessarily: The myocardial perfusion is designed so we can "surmise" the blood flow to the arteries of the heart by differential distribution of a dye. The pictures will not show the lungs and is not designed for the pulmonary vascular distribution.