Magnetocardiography (MCG) has emerged as a sensitive and precise method to diagnose cardiovascular diseases, providing more diagnostic information than traditional technology. However, the sensor limitations of conventional MCG systems, such as large size and cryogenic requirement, have hindered the widespread application and in-depth understanding of this technology. In this study, we present a high-sensitivity, room-temperature MCG system based on the negatively charged nitrogen-vacancy ($\mathrm{N}$-$V$) centers in diamond. The magnetic cardiac signal of a living rat, characterized by an approximately 20-pT amplitude in the $R$ wave, is successfully captured through noninvasive measurement using this innovative solid-state spin sensor. To detect these extremely weak biomagnetic signals, we utilize sensitivity-enhancing techniques such as magnetic flux concentration. These approaches have enabled us to simultaneously achieve a magnetometry sensitivity of $9\text{pT}{\text{Hz}}^{-1/2}$ and a sensor scale of 5 mm. By extending the sensing scale of the $\mathrm{N}$-$V$ centers from cellular and molecular level to macroscopic level of living creatures, we have opened the future of solid-state quantum sensing technologies in clinical environments.

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• Magnetometry
• Optical pumping
• Quantum measurements
• Quantum sensing
• Nitrogen vacancy centers in diamond
• Medical imaging
• Optically detected magnetic resonance