My age 58, 181mm hight, 67kg, I have 3 stents in 2 major heart vains and 2 more balooned to 2 other minor vains. operation is on 28 SEP 2011, 2 monthes ago, heart attacked on 26 SEP 2011. During my exercise on Trade Mills, walking-running machine, What should be maximum heart rate or suitable heart rate during my exercises that I should achieve, or I should reduce my speed of walking so it will not over work or damage my heart?