Remove heading in tabs

I hope someone can help. I used the codes below to remove the heading within the tabs on single product panel. Worked well for product description and additional information tab. However I cannot figure out how to do the same for the reviews tab. Your help would be appreciated.

/**
 * remove on single product panel 'Product Description' since it already says it on tab.
 */
add_filter('woocommerce_product_description_heading', 'isa_product_description_heading');
function isa_product_description_heading() {
    echo '';
}  

/**
 * remove on single product panel 'Additional Information' since it already says it on tab.
 */
add_filter('woocommerce_product_additional_information_heading', 'isa_product_additional_information_heading');
function isa_product_additional_information_heading() {
    echo '';
}

http://wordpress.org/plugins/woocommerce/