Oppai Heart: Kanojo wa Kedamono Hatsujouki!?
Japanese title: おっぱいハート～彼女はケダモノ発情期ッ!?～
Type: OVA
Source: Visual novel
Episodes: 2
Status: Finished Airing
Aired: Oct 28, 2011 to Feb 24, 2012
Duration: 28 min per ep
Rating: Rx - Hentai
Studios: Nihikime no Dozeu
Genres: Hentai

Ryuya has an older sister, Miya.  He lives a peaceful school life with his friends.  But one day, he and his friends accidentally drink a medicine juice.  Once you drink it, you'll become sexually sensitive and get excited.  The breasts of the girls who drink it will get bigger and they will need to have sex to cool down.  Also, to make a vaccine, they will need to get pregnant.  Ryuya starts having sex with the girls to cool them down and make a vaccine.

(Source: ErogeShop)