The Bundesliga giants' return to action with a thrilling 4-3 victory on Saturday was hard work, according to the coach, although Neven Subotic was just delighted to be back
Pierre Emerick Aubameyang, Henrikh Mkhitaryan and Joseph-Claude Gyau scored four goals between them to see off the threat from the 2.Bundesliga club.
Klopp was pleased with their attacking threat and, despite slamming Dortmund's errors, and stressed that his side's opponents had been preparing for competitive matches for longer than his own team have been.
"In one form or another, today was real torture, but it was just so everyone can get back into it," Klopp told Ruhr Nachtrichten after the game. "We have created great goals, but also made stupid mistakes.
"It has to be noted, though, that Heidenheim start their league season in two weeks while we are five weeks off."
BVB defender Neven Subotic made his return from injury against Heidenheim after a gruellling eight months on the sidelines and he conceded that being back on the pitch was a tricky prospect at times due to the length of time he has been off it.
"I knew that this moment will eventually come," he said. "It felt like a small child learning to ride a bike for the second time.
"The first quarter of an hour felt like two minutes, but it was nevertheless worthwhile. Training cannot replicate matchday situations."