Sure, speed and heroin would be a poor man's speedball, not quite the same as coke and heroin but close enough to produce a similar effect. You'd need to try them both to work out the subtleties, what differences there are between the two.
Mr. Scagnattie is right to warn you. If you dose the speed too high that can mask the effects of the opiate, so you take more opiate to get it up to the high you want. If the speed suddenly crashes cos it's a short acting kind or you get the timing out of step that can leave you awash with dangerous levels of the opiate and that way lies OD territory.
As well as what you're taking exactly at what sort of dose, what ROA you using? Any which way treat with caution, start with low doses of each so you get used to effects, can gauge what feels safe, what doesn't as the up and down of each changes over time.