Hello and thanks for the query
Yes your father can take full walk but don't try to compete with others, do as much walk as his body allows. As the medication started for the blockage in the artery
it will not not harm you untill you get proper medicine and follow diet chart and life style changes.
Headache is due to the medication you are taking it will resolve in few days. till than take Paracetamol
for pain. if pain does't subside in 10-15 days consult your doctor and review medicine.
Certain precautions and diet that you have to follow is:
1. Daily exercise for about one hour.
2. Maintain your weight according to your height
3. Check your Lipid profile
once in six month
4. Avoid fatty, oily and junk food
5. use baked food
6. Control your sugar if your are diabetic
7. Stop smoking
The effects are to control BP, get the blood thin so that it cant increase the blockage.You have said the BP is high so consult your doctor again and review your medications.