BEIJING, Nov. 24 -- Chinese Olympic and world swimming champion Sun Yang had failed a doping test and been banned for three months, China Anti-Doping Agency (CHINADA) told Xinhua on Monday.

The star swimmer tested positive for stimulant trimetazidine on May 17 during the national championships.

Sun waived his right to have the B sample tested but defended himself in a July hearing, saying it was a substance in the prescription drug Vasorel he was taking to treat a heart condition and he wasn't aware it was prohibited.

Trimetazidine is able to increase coronary flow reserve and was added to the prohibited list in January 2014.

"I have been tested numerous times during years of training and competition and I had never failed once before," said Sun on Monday, the Zhejiang native, who was also fined 5,000 RMB (about 816 U.S. dollars) with his national 1,500m freestyle title deprived.

"I was shocked and depressed at that time, but at the same time it made me cherish my sporting life even more. I will take it as a lesson and be more careful in the future."

The Zhejiang Swimming Association said the provincial association and some related officials were also punished by the Chinese Swimming Association.

The Chinese swimming body decided to cut Sun's ban to three months because the swimmer "proved with sufficient evidence that he did not intend to cheat," explained Zhao Jia, deputy director of CHINADA.

"But his failure to inform the doping control official should be punished all the same," he added but didn't specify.

Both Sun and Zhejiang team doctor Ba Zhen failed to file the therapeutic use exemption when Sun took the test. Sun had been taking Vasorel from time to time since 2008 when he started to suffer heart palpitations, according to CHINADA.

Along with Sun Yang, CHINADA also announced six other positive cases in its quarterly report on its official website.

"Sun is the most famous athlete in China and is known in the world, which means we need to handle his case with great caution. This is huge bad news but we will not cover it up," said Zhao.

"We announce positive cases and test statistics in our quarterly reports just as WADA requires," he added.

Zhao said the Chinese agency had been burdened with a heavy task -- 9,900 doping tests conducted in six months -- and spent a lot of time sorting out statistics.

"We have to wait until the handling of a particular case has been closed," he said.

"That's why we did not release the reports for the second and third quarters until now," he added.

Sun secured his position as a superstar when he won two gold medals at the 2012 Olympics and setting the world record for the 1,500 meters.

The three-month suspension ended on Aug. 17, before Sun's participation in the Incheon Asian Games in September, where he won three gold medals.