How can a heart of human work if one of its valve is not working?
It is not possible that one of the valve is completely closed and the person is still alive without being in ICU. I think what the doctor was trying to communicate to the patient was that one of the valves is in the process of complete closure. There are three main types of diseases associated with heart valves :-

1- Blood flows backwards
2- Heart valve opening becomes narrow
3- upper condition may lead to complete closure

For details see the following link:-

http://www.nhlbi.nih.gov/health/health-topics/topics/hvd
http://en.wikipedia.org/wiki/Pulmonary_atresia

Hope you understand. :)