It appears that four passages of the Wikipedia entry on the MP insulted him so badly he went to court to prevent anyone from seeing them.
German media reporting on the story have not repeated the passages, saying that they might also be affected by legal action.
Thorsten Feldmann, lawyer for Wikimedia eV, which runs Wikipedia in Germany, told Spiegel Online that the passages largely concern Heilmann's professional and political development.
Heilmann was a member of the ruling East German socialist unity party, the SED, and after reunification, joined its successor party, the PDS. In September 2005 he became an MP for the Left party, representing the state of Schleswig-Holstein.
Shortly afterwards Der Spiegel magazine exposed his past membership of the East German secret service, the Stasi, which he later admitted to concealing.
Feldmann said the Wikipedia site could remain blocked for up to four weeks until a court hearing can be arranged, but said that an appeal would be made on Monday to reverse the injunction.
Users wanting to use the German version of Wikipedia can reach it via de.wikipedia.org – and even read an entry about Heilmann.