The Heart of the Matter: How mRNA Vaccines Can Affect the Human Heart is a groundbreaking manifesto written in plain, accessible language to explain one of the most misunderstood medical realities of our time: the connection between COVID-19 mRNA vaccines and heart inflammation. Richard Sweeney takes readers step by step through the basics of how the vaccines work, why the spike protein is not harmless, how lipid nanoparticles spread throughout the body, and why these mechanisms can sometimes inflame the heart. Blending science with human stories, this book separates fact from conspiracy and empowers readers to understand risks, recognize symptoms, and demand honesty in medicine. More than a medical explanation, it is a call for transparency, compassion, and trust in science that does not silence the truth.