(a) Representative optical and electrical signals acquired simultaneously from the corresponding numbered electrode locations on a Langendorff-perfused rabbit heart. Scale bar: 7 mm.
(b) Top: schematic illustration of a representative optical action potential (OAP), unipolar electrogram (EG) and position of the activation time, defined as

for the OAP and

for the EG. Bottom: correlation of electrical and optical activation times for hearts tested in a variety of states.
(c) Interpolated spatial activation maps determined from the electrical and optical measurements. Top: heart paced by the red pair of electrodes on the membrane. Bottom: sinus rhythm.
(d) 3D mapping of electrical signaling from both the anterior and posterior surfaces of the heart. Interpolated spatial maps of electrical activation time are projected on a representative rabbit heart geometry, for purposes of visualization. Scale bar: 7 mm.