I smoked right up to the time I had my Heart Attack,,never noticed it causing me problems except once when i smoked Green Crack,,that Weed messed with my ticker. Had it beating outta my chest. I was fine with Indicas. I started smoking one week after my Triple Bypass with no problems. Weed actually brings my BP down,,which is good for most PPL,,unless it gets real low. Mine this morning was 98/70,,and I feel great. The only problem I see is if your Dad is having that much problems,,I wouldnt take the chance in Lowering your DADS BP to much since his Heart is not pumping good as it is. My Heart did not have ANY damage because I was 5 mins from the Hospital,,but your Dad already has Damage,,so he probably should not smoke and take the Chance in an Overload(Spike it Heart Beat) or Under-load( BP to low) on his Heart.