They’re pronounced differently (although there’s a difference between British English and American English but for these that difference is quite consistent and you just omit the r):

horse [hɔːs]/[hɔːrs] - worse [wɜːs]/[wɜːrs]

cord [kɔ:d]/[kɔːrd] - word [wɜːd]/[wɜːrd]

How do horse and worse rhyme?