Some hearts follow logic. His never strayed from it. Dr. Ethan Cole has spent his life believing in control—of his work, his emotions, and the rhythm of every beating heart he's ever monitored. As one of London's most sought-after cardiologists, he doesn't have time for distractions. Especially not the kind that come with wild smiles, late-night conversations, and the chaos of a woman who refuses to stay still. But then Sienna Harper stumbles—literally—into his life. A free-spirited travel photographer with a heart that beats to its own reckless rhythm, Sienna has never been one to settle. The world is too big, life is too short, and love? Love is just another thing she can't afford to hold onto. When a medical mishap forces her to slow down, she ends up crashing into Ethan's meticulously controlled world. And to her utter delight—and his absolute horror—she refuses to play by his rules. She fills his silent apartment with music and paint-stained fingertips. She challenges his routines, his need for distance, his fear of wanting something he can't control. And the most dangerous part? He lets her. Because the more time they spend together, the harder it becomes for Ethan to ignore the truth: Some hearts don't follow logic. Some hearts leap. Some hearts risk everything. And for the first time in his life, his just might be one of them. But Sienna doesn't stay. She never stays. And when the time comes for her to leave, Ethan will have to make a choice: Let her go and pretend she never mattered—or break every rule he's ever lived by to fight for the only woman who ever made him feel alive. A slow-burn, grumpy vs. sunshine contemporary romance filled with electric chemistry, emotional depth, and a love worth taking the ultimate risk for, The Rule of Heartbeats is a story about falling, fighting, and finally choosing the kind of love that doesn't let go.