im not sure about the heart conditions....but be careful, especially with such a small dog. just imagine loosing a bit of control over the bike and accidentally hitting the dog....or if she runs in front of the bike...it happens. my husband runs our pitt on his dirt bike (great exercise) the one day he didn't wear a helmet our male decided for some reason or another to cut right in front of the bike and my husband crashed...broke his jaw...so yeah, be careful