How to export variables on remote machine through ssh.

Hello experts,

I need ur help on solving this problem.
I am writing a automation tool that runs several shell scripts on different remote hosts using ssh. These scripts need various pre-defined variables to run. I want to provide these variables to the script by exporting these variables after doing ssh and then run the script that use it, like this:

a=10
ssh -l $user $host "export myVar=$a; cd $myDir; ./myScript.sh"

this doesn't work, as probably the ssh shell might not understand the export command.

Can anybody please tell me how shall i solve this problem.

Thanks.
Gajendra