For doctor Zhang Weida, the Tibet autonomous region is not only a holy land filled with blue skies and vast grasslands, but also a high-risk place for congenital heart disease.

Over the past two years, Zhang, director of the cardiothoracic surgery department of the General Hospital of Guangzhou Military Command of the People's Liberation Army, has traveled several times to remote Tibetan counties and Lhasa, the region's capital, to give free medical checks to about 20,000 children.

"The region is highly vulnerable to congenital heart disease due to its high altitude," Zhang says.