I am not so sure this tactic will have the intended effect. Foetal heart beats don't sound like adult heart beats they sound like an old-fashioned steam train or a galloping horse so it won't necessarily resonate in the macabre way these pro-lifers hope it will.
It's often indicative of pro-lifer types that they don't understand basic aspects of the gestation process and suggest stupid stuff like this. They don't seem to understand that mother nature has put in place bio-mechanisms to stop human females from freaking the fuck out at the experience of pregnancy and labour, and seem to think that showing women pictures of foetuses at 18 weeks gestation or playing them train noises is somehow going to make them think of bunnies and fluffy kittens, rather than aliens or the man/machine interface.