My mother had undergone angioplasty in October as she suffered from a mild heart attack. Doctors have advised her to walk for at least 30 minutes. She is suffering from Diabetes as well. Her age is 57 years. Both diabetes and BP is under control. But when she walks for 3 rounds in the park, she gets a mild pain near chest and shoulder for a few seconds. When she sits, it goes off and after that she can walk for another 3 rounds without pain. Any cause of concern?