Not quite as good though. The above will let just know whether you have the extension, but not whether you have the patched version, which can also be done from

Not quite as good though. The above will let just know whether you have the extension, but not whether you have the patched version, which can also be done from the CLI by using: echo -e "quit\n" | openssl s_client -connect server.com:443 -tlsextdebug 2>&1 | grep heartbeat (as suggested someone in another thread here). That will answer Yes to a patched OpenSSL. The OP's site actually attempts a (mild?) exploit of this.