The last major revision of the Garmin Connect web site provided a serious advancement in its usability, but the addition of one feature could enhance that even further. That would be the addition of an Average Heart Rate column on the Details page next to the Avg Pace column. There is plenty of room. Obviously the Split, Distance and Avg Pace columns are much wider than they need to be, so it would be a simple matter to add Avg HR.
I realize that this information is on the splits page, but so is the information provided in the other columns. Having the Avg HR on the Details page would prevent an extra server hit to have to go to the splits page. Additionally, the Details page is conveniently more concise.
(I'd be happy to code it for you. :) )