I have lower back pain and when I start walking it hurts then pain in both calves starts making it very difficult to walk any distance.  I had open heart surgery in September last year and I am now on warfarin for life so its unlikely to be a clot causing the problem????? I am 49 yrs old and been active until surgery.
No there is no such reason of having pain BCZ of surgery might there is any degeneration of your vertebra back pain can be the reason because of body weight, injury or spine itself. Your calves' muscle may be tight that's why it hurts apply hot pack on calves muscle and back for 10-15 mins. Do ankle toe movement. Stretching of your calves' muscle will also help back exercises in later when pain subsides will also help ultrasonic and laser therapy will help you a lot avoid brisk walk for few days till pain subsides get a check-up also