I'm in the exact same boat as you. Resting heart rate is around 90 (normally in 70s), and using both MK (12.5 mg) and SD (6.25 mg). Low doses for both, but I retain a ton of water on MK, and SD's strength doesn't need explaining.
Really hope to run this for 4 weeks, and expect good gains. The amount of individual response both in terms of gains, and sides boggles my mind sometimes. I have a buddy who can run 25-30 mg of SD for 4 weeks without experiencing any sides aside from some appetite suppression; and I get BP spikes just reading the word "superdrol".
6.25mg a day? How long have you been running it? Are you noticing gains from it?