I wrote a bash script to check the top 1000 websites and huge percentage of them responded with heartbeat extension (30-40%):

  INPUT=websites.csv
  OLDIFS=$IFS
  IFS=,
  [ ! -f $INPUT ] && { echo "$INPUT file not found"; exit 99; }
  while read rank website
  do
    echo "checking $website for heartbeat..."
    echo -e "quit\n" | /usr/local/bin/openssl s_client -connect $website:443 -tlsextdebug 2>&1| grep 'TLS server extension "heartbeat" (id=15), len=1'
  done < $INPUT
  IFS=$OLDIFS

You can download a list of top 1 million websites from Alexa and Quantcast: http://www.seobook.com/download-alexa-top-1-000-000-websites...

Chinese websites timeout on port 443 so you'll have to skip them.

Keep in mind that you have to run this with OpenSSL v1.0.1 and above. Running it on a stock OS X Mavericks install will not detect the extension because v0.9.8 of OpenSSL is installed.

At least in my Bash (4.2.25(1)), there seems to be a difference between "2>&1|" and "2>&1 |" – the latter works as expected, whereas the former doesn’t give any output.

   $ echo -e "quit\n" | openssl s_client -connect chubig.net:993 -tlsextdebug 2>&1| grep 'TLS server extension "heartbeat" (id=15), len=1'
   $ echo -e "quit\n" | openssl s_client -connect chubig.net:993 -tlsextdebug 2>&1 | grep 'TLS server extension "heartbeat" (id=15), len=1'
   TLS server extension "heartbeat" (id=15), len=1
   $ 

Does anybody know why?