Individuals involved in intense resistance training present with increased absolute left ventricular (LV) wall thickness and mass and show good systolic responses to isometric exercise. There is no consensus regarding diastolic features and no available information regarding diastolic function in athletes during isometric exertion itself. Therefore, the main aim of this study was to assess diastolic LV function at baseline and during exercise in athletes. The population consisted of 96 men (mean age 29 ± 7 years): 48 weightlifters who trained for 15 to 20 hours/week and 48 sedentary men. All weightlifters had been active for >6 years, including the 6 months before the study. Ultrasound was performed using a commercially available Doppler echocardiographic system. Isometric exercise was performed in the supine position using a standard 2-hand bar dynamometer. The man end-diastolic volumes at rest were 97 ± 6 ml in sedentary subjects and 101 ± 5 ml in weightlifters, increasing to 100 ± 6 and 118 ± 11 ml during exercise (p = 0.06 and p <0.01, respectively). End-systolic volumes at rest were similar in the 2 groups, showing significantly greater reductions during exercise in the weightlifters. The mean absolute LV mass was 167 ± 30 g in sedentary subjects and 202 ± 32 g in weightlifters (p <0.0001). The mean stroke volume increased from 65 ± 7 to 86 ± 7 ml in sedentary subjects and from 70 ± 6 to 107 ± 11 ml in weightlifters (intergroup significance p = 0.05 and p <0.01, respectively). A similar pattern of response was documented for the ejection fraction (i.e., significantly greater increases during exercise in weightlifters). Regarding diastolic indexes, in the weightlifters, the mean peak early velocity at rest was 68 ± 7 cm/s, the mean acceleration rate was 1,242 ± 176 cm/s/s, and the mean deceleration rate was 414 ± 44 cm/s/s. All these values were significantly higher than in sedentary subjects, with further increases during exercise (p <0.0001). In weightlifters, the mean peak atrial velocity at rest was 37 ± 6 cm/s, the mean acceleration time was 55 ± 4 ms, the mean isovolumic relaxation time was 63 ± 3 ms, and the mean deceleration time was 164 ± 4 ms; these values were lower than in sedentary subjects (p <0.0001 for all). In conclusion, intense resistance training leads to enhanced LV diastolic function at rest and during isometric exercise despite the markedly increased LV mass.