Fig. 4: Estimation of the spatiotemporal dynamics of the cardiac current.

a Measured field map at the R-wave peak, superimposed on the contour of the structure of the rat’s heart revealed by optical imaging and magnetic resonance imaging (MRI). The black solid line is a linecut connecting the centres of the observed positive and negative magnetic field peaks. b Vector plots of the electric current density calculated using bfieldtools with a standoff distance of \({d}_{Q}^{{{{{{\rm{NV}}}}}}}=8.1\pm 0.7\) mm. As a guide for an eye, the MRI image is superimposed in greyscale. c Normal component of the electric current density vector with respect to the linecut. The green shaded region shows the uncertainty of the current density estimated from the uncertainty of the standoff distance (one standard deviation) obtained in the dipole fitting. d–f Measured field map (d), estimated electric current density (e), and electric current density across the linecut (f) evaluated at 20 ms after the R-wave peak.