AS and endurance training

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I'm new to steroids and I'm just planning to start a cycle of Deca and/or sustanon to increase strength but I'm not a bodybuilder, I'm a "biathlete" (athletic biathlon's popularity is inscreasing in my country). My sport is power lifting (bench press) and 2 miles running (3,2 km). Does anybody out there know how could be AS effects with high cal dieting and weight training while doing endurance running (I run 4 times a week for 1 hour each time). I know most of you will blame AS intake while doing calories burning exercise but I'll try to make a correct diet. I'd like to know if there could be some serious heart damages considering I'm planning only to make a light 6/8 weeks cycle (i just want to increase my bench press pounds of about 20 or 30).
Please let me know what u think. If anybody there know something useful about "steroids and endurance training", well I'm the guy u have to tell it...