add_filter( 'avf_google_heading_font', 'avia_add_heading_font');
function avia_add_heading_font($fonts) {
    $fonts['PT Sans Narrow'] = 'PT Sans Narrow:400,700';
    $fonts['PT Sans'] = 'PT Sans:400,700,400italic,700italic';
    return $fonts;
}

add_filter( 'avf_google_content_font', 'avia_add_content_font');
function avia_add_content_font($fonts) {
    $fonts['PT Sans'] = 'PT Sans:400,700,400italic,700italic';
    $fonts['PT Sans Narrow'] = 'PT Sans Narrow:400,700';
    return $fonts;
}