How fast can a sedentary lifestyle deteriorate heart health? Is one year of sedentary lifestyle enough to cause high blood pressure or other heart issues? I am starting back walking but heart beats really hard with extreme bp response. 28 y.o

Unlikely. Heart issues would be unlikely in your age group, but muscle deconditioning does occur in a couple of weeks of no exercise. Generally high blood pressure is caused by other factors like weight gain,chronic stress,excessive salt, caffeine or alcohol intake. If palpitations occur it's best to have a physician evaluate you and order appropriate tests such as EKG, thyroid panel, treadmill stress test.