Spontaneous diastolic calcium oscillations were induced by 15 s of rapid pacing followed by a pause. Shown in each panel are the electrocardiogram (ECG, top) and intracellular calcium (bottom) recorded from a single site on the epicardium under control conditions (A), control at a faster pacing rate (B), and with ryanodine (C). Under control conditions at 210 beats/min (A), a spontaneous diastolic calcium oscillation was observed (arrow) after termination of rapid pacing. S1, rapid pacing. A more rapid heart rate [330 beats/min (bpm)] resulted in a triggered beat (TA, B) with multiple oscillations of diastolic calcium (arrows). Ryanodine (1 μM, C) abolished TA and any spontaneous calcium oscillations during diastole.