The researchers found the hearts, which likely belonged to wealthy noblemen, when they were excavating the ruins of the Convent of the Jacobins in Rennes, France. Since the excavation began in 2011, they have found some 800 graves, along with these five embalmed hearts, each encased in heart-shaped urns made of lead. Slowly and carefully, a team of experts in many different disciplines removed the hearts from their urns and unwrapped the embalming material. They took MRI and CT images of the hearts, identifying the valves and chambers in four of them (one was too poorly preserved to show much). Once the researchers rehydrated the tissue, they took more scans and dissected the hearts to look closely at the muscle and tissue.