4.5 stars 
 Sometimes a book just kind of hits you in the gut and that is exactly what happened with The Heartbeat Hypothesis. I'm extremely impressed by new author Lindsey Frydman and this story is unique and refreshingly honest and while there was a bit more angst than I normally enjoy, with these characters it was fully warranted. Gut wrenching yet hopeful; The Heartbeat Hypothesis was an emotionally charged and complex story. 
 This review is going to be short because this is one of those books that you have to experience so the less said about it the better. College freshman Audra Madison is lucky to be alive and I mean that seriously and when she discovers that her heart donor's older brother, Jake Cavanaugh, attends the same school, she is determined to seek him out and asks him to help her recreate a series of photos his younger sister did on her Tumblr page as a tribute to her. The set out to do these photos but in the meantime, they also spend time together in other ways (non sexual ways) and Audra begins to develop feelings for him while he remains somewhat aloof and at times even a bit mean. 
 Both these young adults (18 and 21) have been through more than many adults and while Audra seems a bit immature which I'm sure is due to her heart condition and her parents need to suffocate her, Jake seems much older than his years and as this story unfolds we find out why. 
 I enjoyed the way their friendship built and that over time they began to open up to one another about their lives. While I do felt Audra made some poor choices in judgment, I could also understand her frustration with the way Jake always seemed to change the subject or leave when things got tough. While I realize he didn't "owe" her anything and tried to tell her he wasn't good for her, he also didn't seem to discourage her attentions. He was the master of mixed signals. 
 This was not an easy story; it deals with loss, tragedy, depression, abuse, and two young people trying to deal with it all. These characters are put through the wringer and learning to navigate through the myriad of complications and turmoil takes a toll not only on them personally but on their fragile relationship. However, through all the darkness they manage to find the light. 
 The Heartbeat Hypothesis was poignant, refreshing, and an exceptional first book for author Lindsey Frydman. 
 Review copy provided for a voluntary review.