in a nutshell, yes; cocaine is cardiotoxic after all. and that cocktail very well could be a recipe for an OD with 3 potent CNS drugs working beside each other with the cocaine on top.
it's tit for tat. the pull of the downers may not have you feeling the coke adequately to your standards having you dose more creating more unnecessary strain on your heart. after the coke wears off and the downers predominately take over the high you could then run into CNS depression.