[WordPress] Code from our blog post A MailChimp Opt-in Field for Contact Form 7 - http://www.limecanvas.com/a-mailchimp-opt-in-field-for-contact-form-7/

code-snippet-1.php

[ text* your-name 58/ ]
[ email* your-email 58/ ]
[ checkbox mailchimp-optin default:1 use_label_element "Subscribe to our newsletter" ]

code-snippet-2.php

/* MailChimp CF7 integration
* Uses <theme>/includes/MCAPI.class.php
*/
function wpcf7_send_to_mailchimp($cfdata) {
  $formtitle = $cfdata->title;
  $formdata = $cfdata->posted_data;
  // Opt-in field checked?
  if ( $formdata['mailchimp-optin'] ) {
    $names = explode(' ',trim($formdata['your-name']));
    $firstName = $names[0];
    $lastName = '';
    if (count($names)>1){
      // more than one word in name field
      $lastName = array_pop($names);
    }

    $send_this_email = $formdata['your-email'];
    $mergeVars = array(
      'FNAME'=>$firstName,
      'LNAME'=>$lastName
    );
    // MCAPI.class.php needs to be in theme/includes folder
    require_once('includes/MCAPI.class.php');

    // grab an API Key from http://admin.mailchimp.com/account/api/
    $api = new MCAPI('YOURAPIKEY');

    // grab your List's Unique Id by going to http://admin.mailchimp.com/lists/
    // Click the "settings" link for the list - the Unique Id is at the bottom of that page.
    $list_id = 'YOURLISTID';

    // Send the form content to MailChimp List without double opt-in
    $retval = $api->listSubscribe($list_id, $send_this_email, $mergeVars, 'html', false,true);
  }
}
add_action('wpcf7_mail_sent', 'wpcf7_send_to_mailchimp', 1);

I replaced the API key and Listing ID.But seems it doesnt work.Subscribers didnt added to Mailchimp list.Please help me to solve this!