Hypothermic hyperkalemic cardioplegic arrest (HHCA) is a commonly used technique of cardiac surgery. However, left ventricular (LV) pump dysfunction can occur following reperfusion and rewarming, the cellular basis for which remains unclear. We hypothesized that the prolonged membrane depolarization due to HHCA causes increased myocyte intracellular free calcium ([Ca 2 + ] i ), which is associated with alterations in contractile performance. Accordingly, time dependent changes in [Ca 2 + ] i were measured in porcine LV myocytes (n = 30) using calcium fluorescence. Measurements were sequentially recorded in the same myocyte: during Normothermia (cell media, 15 min, 37 C), HHCA (crystalloid cardioplegia, 60 min, 12 C, 24 mEq K + ), and subsequent Reperfusion (cell media, 15 min, 37 C). In light of the fact that HHCA caused increased [Ca 2 + ] i , we next examined myocyte shortening velocity at Normothermia (n = 268) and following HHCA and Reperfusion (n = 231) using video microscopy. Myocyte contractility following HHCA and Reperfusion was decreased compared to Normothermia (66.6 +/- 2.1 vs 33.6 +/- 1.2, μm/s, p < 0.05). Summary: This study demonstrated for the first time that HHCA causes a prolonged elevation in myocyte [Ca 2 + ] i which is associated with contractile dysfunction following reperfusion. Thus, fundamental mechanisms contributing to the transient LV pump dysfunction following HHCA include alterations in calcium homeostasis and myocyte contractile dysfunction.