Arizona used a two-drug protocol for Wednesday's execution of Joseph Rudolph Wood, who had been sentenced to die for the 1989 deaths of a former girlfriend and her father. Witnesses saw Wood gasp and snort for an hour and 40 minutes after the execution drugs were injected in his veins. While no one knows why Wood's execution lasted so long, a common denominator for three lengthy executions this year is midazolam, a sedative often given to patients prior to surgery. Midazolam's side effects can include serious breathing problems and cardiac arrest. Oklahoma inmate Clayton Lockett died 43 minutes after his execution began in April — of an apparent heart attack after the state's prison's chief directed the executioner to stop administering lethal doses of three drugs: midazolam, vecuronium bromide and potassium chloride. Potassium chloride is used to treat potassium deficiency but is used in executions to stop the heart.