I have a pacemaker. My last 6 month check showed when I get above a 80 rate, I go into heart block. The graph showed almost all 70-80 rythm. Very little above the 80. I try to exhert myself and get very tired and stressed. How hard can I push myself? I try to do gardening (shovel, hoe, rake, bend, weed...) Is this safe?I