Fig. 2

Examples of normal heart rhythm and ectopic heartbeats in wildtype mouse embryos. A Pulsed-wave Doppler tracing across the mitral and aortic valves showing normal heart rhythm at E18.5. During each cardiac cycle, there is a biphasic ventricular inflow pattern (E’ and A’) followed by a monophasic ventricular outflow pattern. B Pulsed-wave Doppler tracing at E13.5 showing multiple premature atrial contractions (PAC, yellow arrows), i.e. extrasystoles, all followed by compensatory pause [illustrated by the elongated passive filling phase (red arrows)]. C Pulsed-wave Doppler tracing at E18.5 showing a PAC followed by a tachycardia with a monophasic ventricular inflow pattern (only A’). E’: passive ventricular inflow due to ventricular relaxation; A’: active ventricular inflow due to atrial contraction; PAC: premature atrial contraction; S’: ventricular outflow due to ventricular contraction