Fig. 3.

Summary of Ca_i²⁺ and APD alternans at different temperature conditions. A and B: Ca_i²⁺ alternans (A) and APD alternans (B) at physiological temperature (PT), room temperature (RT), and cold temperature (CT). Left: light shaded regions show the incidence of monolayers with no alternans (NA monolayers), medium shaded regions show the incidence of monolayers with spatially concordant alternans (A_C monolayers), and dark shaded regions show the incidence of monolayers with spatially discordant alternans (A_D monolayers). Values in bars are numbers of monolayers. Right: plot of PCL showing the transitions from the window of 1:1 response (light shaded regions) to the windows of 2:2 response, consisting of regions of spatially concordant alternans (SCA; medium shaded regions) and spatially discordant alternans (SDA; dark shaded regions). These regions, in turn, define the alternans vulnerable window (AVW; medium and dark shaded regions together) and spatially discordant alternans vulnerable window (AVW_D; dark shaded region). Error bars are not shown but are given in Supplemental Tables S1–S3. C and D: plots of mean PCL_C, PCL_D, and MCL for Ca_i²⁺ (C) and APD (D) alternans. Solid lines connect measured values of MCL, and dashed lines connect measured values of PCL_C and PCL_D. Extrapolated values for PCL_C and PCL_D, determined from Q₁₀ values and Eq. 1, are plotted for PT. Error bars show SEs.