Heidfeld crashed out of the race after making contact with Buemi's right rear tyre, with the Swiss having to pit to changes his tyres.
The FIA stewards deemed Buemi was at fault and have imposed a five-place grid penalty for next weekend's race.
"Heidfeld drove into me at the chicane and I got a puncture on my right rear," said Buemi. "So I had to pit and change tyres, which compromised our strategy even more and with no rain, that was really it.
"It has been a disappointing weekend in which we cannot be satisfied with our performance, therefore all we can do is look ahead to the Hungarian Grand Prix and at least we don't have long to wait for that."
The penalty comes after Buemi was disqualified after yesterday's qualifying following a fuel irregularity.
Heidfeld was given a drive-through penalty for a crash with Paul di Resta at the start of the race, but the German did not have time to serve it. The FIA said it will not take any further action against the Renault driver.