Electrophysiology of atrial (aEHM) and ventricular (vEHM) engineered human myocardium. (A) Schematic of the EHM culture procedure used in this study. (B) Representative action potentials (AP) elicited at 1 Hz in aEHM (A, left) and vEHM (V, right) before (baseline) and after application of the M-receptor agonist carbachol (CCh, 10 µmol/L). (C) AP duration at 20, 50, and 90% repolarization (APD20, APD50 and APD90, top left), AP amplitude (APA, top right), upstroke velocity (dV/dtmax, bottom left), and resting membrane potential (RMP, bottom right; atrial: n = 13/3, ventricular: n = 5/2). (D), Percentage change of APD90 following CCh application. (E), Percentage change of RMP following CCh application (atrial: n = 6/2, ventricular: n = 5/2). Data are mean ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001 vs. aEHM using unpaired Student’s t-test or Welch’s t-test (E). n/N = number of recordings/EHM.