Magento Cron job working – AOE Scheduler no heartbeat

I am using my dev site to test an abandoned cart email through MageMonkey/Mandrill. I believe I already have the cron job already configured as other transactional emails send without a problem (maybe this assumption is wrong?).

I also installed the AOE Scheduler and it displays all of the correct cron jobs. After I manually run the heartbeat and generate a schedule – nothing else runs and I get the notice that the "heartbeat is older than xx minutes."

I'm honestly not sure where my issue is – whether it is because I am in the dev site (shouldn't be because other emails send), the cron job configuration or the AOE Scheduler, etc.

In my magento admin under configuration I have the following:
generate schedules every 15
schedule ahead for 30
missed if not run within 45
success history lifetime 1440
failure history lifetime 1440
heartbeat taske */5 * * *

I am using Magento 1.7

Thanks everyone! This is pretty new to me

Here is my cron.php file –

require 'app/Mage.php';

if (!Mage::isInstalled()) {
    echo "Application is not installed yet, please complete install wizard first.";
    exit;
}

// Only for urls
// Don't remove this
$_SERVER['SCRIPT_NAME'] = str_replace(basename(__FILE__), 'index.php', $_SERVER['SCRIPT_NAME']);
$_SERVER['SCRIPT_FILENAME'] = str_replace(basename(__FILE__), 'index.php', $_SERVER['SCRIPT_FILENAME']);

Mage::app('admin')->setUseSessionInUrl(false);

umask(0);

try {
    Mage::getConfig()->init()->loadEventObservers('crontab');
    Mage::app()->addEventArea('crontab');
    Mage::dispatchEvent('default');
} catch (Exception $e) {
    Mage::printException($e);
}