Hi,
Thanks for the query.
The amount of exercise you should do will depend on your tolerance limits. It is not advisable to overdo exercise if you are not tolerating it. That being said, if it's your first day of exercise, you can start with 20 minutes a day for 5 days a week. You may slowly and gradually increase the duration and frequency of exercise based on your tolerance and needs.
Yoga is a good form of exercise for general well being and healthy heart. However if your weight is above normal limit, I would suggest you to add at least 20 minutes of brisk walking or jogging along with Yoga.
It is essential that you keep your weight, blood sugar, blood pressure and cholesterol levels for a healthy heart. Avoiding smoking and alcohol also applies.
Hope this answers your question. Let me know if you need clarifications.
Good luck!!