A jury in Los Angeles Wednesday cleared Merck of responsibility for the heart attack of Stewart Grossberg, a 71-year-old retired construction manager who took Vioxx for two years. Lawyers for Grossberg tried to persuade jurors that he suffered a heart attack as a result of taking Vioxx on a sporadic basis from 1999 until 2001 at age 66. But during the trial, Merck successfully argued that Grossberg had high-cholesterol levels, atherosclerosis and a family history of cardiac problems that led to his heart attack. Including last week’s verdict, Merck has won five of the eight Vioxx cases that have gone to trial. A ninth case is under way in federal court in New Orleans.