On Feb. 10, Valeant Pharmaceuticals International Inc. bought the rights to a pair of life-saving heart drugs. The same day, their list prices rose by 525% and 212%.

Neither of the drugs, Nitropress or Isuprel, was improved as a result of costly investment in lab work and human testing, Valeant said. Nor was manufacture of the medicines shifted to an expensive new plant. The big change: the drugs’ ownership.

“Our...