Visual sensory memory (VSM) has a high capacity, but its contents are fleeting. Recent evidence that the breadth of attention strongly influences the efficiency of visual processing suggests that it might also modulate the effective capacity of VSM. We manipulated the breadth of attention with different cue sizes and used the partial-report technique to estimate the capacity of VSM. Whether attention was deployed voluntarily or captured by a salient cue, narrowly focused attention increased the effective capacity of VSM. This study reveals, for the first time, a direct influence of the breadth of attention on the effective capacity of VSM.