How to unset an environment variable set by `export` in Linux

To unset an environment variable set by `export` in Linux, use `unset` as follows:

$ export LS_HEAP_SIZE=4g
$ echo $LS_HEAP_SIZE
4g
$ unset LS_HEAP_SIZE
$ echo $LS_HEAP_SIZE

$

Reference:
http://stackoverflow.com/questions/6877727/how-do-i-delete-unset-an-exported-environment-variable