My father had a cva in october 2012. no one was able to give the cause. he doesn't have htn. he has knownn dm type 2 but they did a a1c which was 5. what should be done?

Many reasons: A stroke maybe cause by many reasons. I'm assuming this wasn't a hemorrhagic stroke because that would be easily seen on ct scan. Every stroke pt should have an echocardiogram, a carotid artery ultrasound, a lipid panel to check for high cholesterol, and an mra of the brain to evaluate for any blockages in the arteries of the brain. He should follow with a neurologist for further evaluation.

A few other tests: Other than the routine tests all ready mentioned , other test for hypercoaguable state , tee, and possibly a implantable loop recorder may be helpful. Mra with contrast and blood work for vasculitis

A few causes : Consider elevated triglycerides, homocysteine, CRP or sed rate, all can cause problems with blood vessels. Search for distant blood clots (emboli) from heart, aortic arch, large neck vessels (carotids, vertebras), perhaps arterial dissection. Maybe diabetes played a role, but sounds like under terrific control. Other considerations include cadasil, anti-phospholipid antibody syndrome, lupus.