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To improve the current understanding of the impact of resistance exercise on the heart, by examining the acute responses of left ventricular (LV) strain, twist, and untwisting rate (“LV mechanics”).LV echocardiographic images were recorded in systole and diastole before, during and immediately after (7–12 s) double-leg press exercise at two intensities (30% and 60% of maximum strength, one-repetition maximum). Speckle tracking analysis generated LV strain, twist, and untwisting rate data. Additionally, beat-by-beat blood pressure was recorded and systemic vascular resistance (SVR) and LV wall stress were calculated.Responses in both exercise trials were statistically similar (P > 0.05). During effort, stroke volume decreased, whereas SVR and LV wall stress increased (P < 0.05). Immediately after effort, stroke volume returned to baseline, whereas SVR and wall stress decreased (P < 0.05). Similarly, acute exercise was accompanied by a significant decrease in systolic parameters of LV muscle mechanics (P < 0.05). However, diastolic parameters, including LV untwisting rate, were statistically unaltered (P > 0.05). Immediately after exercise, systolic LV mechanics returned to baseline levels (P < 0.05) but LV untwisting rate increased significantly (P < 0.05).A single, acute bout of double-leg press resistance exercise transiently reduces systolic LV mechanics, but increases diastolic mechanics after exercise, suggesting that resistance exercise has a differential impact on systolic and diastolic heart muscle function. The findings may explain why acute resistance exercise has been associated with reduced stroke volume but chronic exercise training may result in increased LV volumes.