hi, thank you for providing the brief history of your father. A thorough cardiac and musculoskeletal assessment is advised, As your father is having a pacemaker, i will advice to under go the free exercises rather going on a treadmill or so. Also, on a treadmill he can only perform the general lower limb and balancing retraining and at his age with the pacemaker, i personally will not recommend. Walking has to be performed in a ground or in park, as it is safe, in ageing the thing to notice is that, ageing people can have frequency of fall at any time anywhere, so no hard objects should stay next to him, and personally i feel treadmill is not safe. Walking in park or ground is safe as if he have a fall also, it will be a mud, so changes of safety is high. Also, in ageing, there is commonest injury of pathological fracture, as the bones become weak as age progresses. Also, general exercises can be performed under the guidance of a physical therapist or also in a group therapy classes. Safety is more important than anything. In my clinical practice, i only recommend free exercises as to regain the cardiorespiratory rehabilitation, neuromuscular rehabilitation and musculoskeletal rehabilitation. We take a duration of 12 weeks and prolong further based on the assessment. I have personally found maximum output from patients health and a great health. I will recommend to look forward with this. Regards Jay Indravadan Patel