Doctor says my heart is "sluggish". what does this mean?

Weak: I imaging that a series of test were done. Like cardiac nuclear imaging, 2d echocardiogram, cardiac catheterization. The nature of the weakness probably quantify by ejection fraction. More than 55% normal. Most common causes are ischemic vs dilated cardiomyopathy. Talk to your doctor for orientation about causes, treatment and rehabilitation process. Lifestyle changes very important.