A1: changes in calcium concentration in cardiac myocytes before and after exposure to caffeine (10 mM) (0.75 ± 0.12 vs. 0.53 ± 0.07, Con vs. Stress, **P < 0.01; 0.75 ± 0.12 vs. 0.57 ± 0.07, Con vs. Con + Caff, *P < 0.05; 0.75 ± 0.12 vs. 0.20 ± 0.06, Con vs. Stress + Caff, **P < 0.01; 0.53 ± 0.07 vs. 0.20 ± 0.06, Stress vs. Stress + Caff, ##P < 0.01). A2: percentage change in calcium concentration (37.72 ± 5.68 vs. 60.02 ± 1.04%, Con vs. Stress, **P < 0.01). B1: percentage change in calcium departure velocity (123.60 ± 6.70 vs. 52.90 ± 5.64, Con vs. Stress, **P < 0.01; 123.60 ± 6.70 vs. 80.54 ± 8.91, Con vs. Con + Caff, **P < 0.01; 123.60 ± 6.70 vs. 24.19 ± 7.34, Con vs. Stress + Caff, **P < 0.01; 52.90 ± 5.64 vs. 24.19 ± 7.34, Stress vs. Stress + Caff, ##P < 0.01). B2: percentage change in calcium departure velocity (33.65 ± 6.97 vs. 56.74 ± 5.11%, Con vs. Stress, **P < 0.01). C1: percent change in calcium return velocity (−99.70 ± 6.88 vs. −49.07 ± 8.07, Con vs. Stress, **P < 0.01; −99.70 ± 6.88 vs. −71.94 ± 8.80, Con vs. Con + Caff, **P < 0.01; −99.70 ± 6.88 vs. −25.69 ± 4.52, Con vs. Stress + Caff, **P < 0.01; −49.07 ± 8.07 vs. −25.69 ± 4.52, Stress vs. Stress+Caff, ##P < 0.01). C2: percentage change in calcium return velocity (23.21 ± 4.42 vs. 50.88 ± 6.92%, Con vs. Stress, **P < 0.01). Values are means ± SE; n = 15.