Sorry. I remembered the facts incorrectly. I know that heise is working together (owning?) with another publisher (d.punkt) and they said about themselves that Springer is invested in them. So I got it mixed up in my brain. Sorry again...
And then there’s Springer[0], one of the largest scientific publishers worldwide, and Springer[1], one of the largest tabloid owners worldwide.
[0] https://en.wikipedia.org/wiki/Springer_Science%2BBusiness_Me...
Heise has a long history as an independent, privately owned publisher, it's still a family-run business: http://www.heise-medien.de/artikel/Geschichte-1357257.html