Calcium spark properties do not depend on the genotype at rs13143308. (A) Ca²⁺ transient from a single spark site. Consecutive 8 × 8 μm images of the calcium spark are shown below the Ca²⁺ transient during its rise and decay (white window area). (B) Enlarged image of the calcium spark in A, recorded at its maximal amplitude. The profile of the calcium spark is shown on the right for each of the four coloured axes outlined in the image on the left. The width of the calcium spark at half maximum was calculated as the average of the four axes. (C) Calcium spark amplitude. (D) Calcium spark duration at half maximum. (E) Width of the calcium spark at half maximum. Values are from the same myocytes as in Figure 2. P-values for the unpaired t-tests (C) or Mann–Whitney tests (D and E) are given above data points and the number of patients is given in parentheses.