A former substitute teacher and a Brooklyn EMT were busted after a five-month investigation revealed they were selling heroin, police sources said.

Lisa Testa, 33, who hasn’t worked for the Department of Education since 2008, was arrested outside of her Bensonhurst home on 2 p.m. Thursday while waiting for her supplier, cops said.

EMT Joseph Meyer, 26, was also waiting for the supplier, Michael Ortiz, 26, outside the same home, the sources said.

The investigation started in December 2013 after detectives received a written statement that claimed the school teacher was addicted to pills and heroin — and was selling the drugs, the sources said.

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