I believe the answer is the Plateau phase of the sexual response cycle. The sexual response cycle has four stages of sexual responding described by Maters and Johnson; that is the excitement, plateau, orgasm, resolution phases. During the excitement phase, the genital areas become engorged with blood. During the orgasm phase, there are muscle contractions all over the body, further increasing breathing, pulse and blood pressure rates; and during resolution phase the body gradually returns to its unaroused state as the engorged genital blood vessels release accumulated blood.