Silent heat occurs when your bitch ovulates but shows no outward signs of being in heat. This means that her vulva won't swell, she produces little to no discharge, and she shows little to no interest in male dogs. Because there are no obvious signs of estrus, many newer owners assume that their bitch has not undergone her first heat cycle yet. To confirm that your bitch is experiencing silent heats, your vet will take blood serum samples for testing. They will test for progesterone and luteinizing hormone (LH) levels. If your bitch's heat is silent, her progesterone and LH will rise as normal to prepare for ovulation. The cause of silent heat cycles in bitches is not clear.