Exeption in thread "http-8080-10" java.lang.OutOfMemoryError: Java

Exeption in thread "http-8080-10" java.lang.OutOfMemoryError: Java

I have an Web application running on my 64-bit windows server 2003, oracle
11G database and apache tomcat 6.0 web server. Application is on live
environment and around 3000 of user using the application,i have been
encountered with Java heap out of memory error but after increasing Heap
space its resolved now again facing same issue, below is the error stack
trace,
Exeption in thread "http-8080-10" java.lang.OutOfMemoryError: Java heap
space Aug 23, 2013 8:48:00 PM com.SessionClunter getActiveSessions
Exeption in thread "http-8080-11" java.lang.OutOfMemoryError: Java heap
space Exeption in thread "http-8080-4" Exeption in thread "http-8080-7"
java.lang.OutOfMemoryError: Java heap space
Please help me and give proper solution that i can apply as my live
application is down. Thanx in advance.