Fig. 2. Ca²⁺ sparks underlie global Ca²⁺ signals in cardiac myocytes. The figure shows a sequence of images of the same ventricular cardiomyocyte taken at 33 millisecond intervals. The left-hand image shows the cell with a low resting Ca²⁺ concentration prior to stimulation. The right-hand image shows that 66 milliseconds after electrical stimulation (marked with ‘lightening zap’ symbol) the cell shows a homogenous Ca²⁺ increase. On the rising phase (middle image), the Ca²⁺ increase can be seen as many focal Ca²⁺ increases (Ca²⁺ sparks).