Cold‐water swimming is a recreational activity that may become a future Winter Olympic event. However, unintentional cold‐water exposure can lead to arrhythmias, changes in electrocardiogram (ECG) appearance, and death. This study sought to characterize cardiac responses to recreational one‐kilometer swims performed in normal and cold‐water. Competitive swimmers (2 male 2 female; age 44±17 years; BMI 24±2) completed a one kilometer swim (22 laps × 75‐foot lengths) under free‐living indoor (25.5°C water and 25.0°C air) and cold outdoor (10.9°C water and 6.5°C) conditions. Continuous ECGs were obtained with a waterproof recording system (Actiwave, CamNtech Inc., Boerne, TX). ECG PR‐, QT‐, and RR‐intervals (sec), ventricular diastole (sec), and heart rate (beats/minute) were measured 8.7±1.7 minutes before the swim, then 0.6±0.2, 3.0±0.0 and 6.4±2.1 minutes after the swim. Data (mean±SD) was analyzed with repeated measures ANOVA with significance if P<0.05. Swimmers completed the indoor and outdoor swim events in 20.7±1.7 and 21.8±1.1 minutes, respectively. For the indoor swim, PR‐interval (sec) at −8.7, +0.6, +3, and +6.4 minutes was 0.12±0.01, 0.12±0.01, 0.11±0.01, and 0.12±0.01, and PR‐interval for the outdoor swim at −8.7, +0.6, +3.0 and +6.4 minutes was 0.13±0.01, 0.13±0.01, 0.13±0.01, and 0.14±0.01 (sec). PR‐interval was significantly longer at +6.4 minutes post cold‐water swim. For the indoor swim, ventricular diastole (sec) at −8.7, +0.6, +3, and +6.4 minutes was 0.37±0.06, 0.22±0.04, 0.30±0.01, and 0.32±0.05 (sec), and for the outdoor swim at −8.7, +0.6, +3.0 and +6.4 minutes ventricular diastole was 0.35±0.08, 0.19±0.02, 0.30±0.04, and 0.24±0.06 (sec). Ventricular diastole was significantly shorter at +6.4 minutes post coldwater swim. No significant changes were observed for QT‐interval, RR‐interval, and heart rate between swim conditions. These parameters were also assessed for the ECG recordings collected during the 20.7±1.7‐minute normal and 21.8±1.1‐minute cold‐water swims to characterize the physiological response during swim exercise. This study of normal and cold‐water one‐kilometer recreational swimmers determined that a waterproof ECG could generate a continuous record of changes in cardiac function. During cold‐water swim recovery (+6.4 minutes) PR interval was lengthened and ventricular diastole was shortened suggesting an influence of temperature on cardiac function.