Two-time Mexican presidential challenger Andres Manuel Lopez Obrador has been hospitalized following a heart problem that required surgery.

His spokesman Cesar Yanez tells The Associated Press that Lopez Obrador is in good health after being admitted to a Mexico City hospital on Tuesday.

Lopez Obrador has refused to accept official results that he narrowly lost the past two presidential elections. In 2006, he paralyzed Mexico City streets with hundreds of thousands of supporters, challenging a ruling that he lost by less than a percentage point to Felipe Calderon.

Lately, Lopez Obrador has led protests against a measure proposed by President Enrique Pena Nieto to open the state-controlled oil industry to private investment.