Helicopter pilot arriving at a hospital heliport; describes a conflict with another helicopter departing. The other helicopter was not visually acquired and the reporter executed a go-around.

Narrative

Inbound to the hospital heliport notified Flight Control of 5 Minute ETE. [I] was advised that another helicopter (helicopter Y) was turning up to depart. Self announced setting up for approach on the common frequency. Heard helicopter Y advise Control departing to the south. Was in a position to observe the approach corridor (primary approach) and the pads at the hospital but was unable to see helicopter Y. Received TCAD alerts and assumed helicopter Y was clear of the pad and enroute to the south because of the time delay since his departure call. [I] heard Control advise helicopter Y that I was inbound. Heard helicopter Y advise Control they were monitoring 'other frequency' and would coordinate with us. [I] called final for the Primary Pad over the River. [I] was advised by Control to hold approach due to helicopter Y departure. Still unable to locate helicopter Y; I executed a go-around straight ahead then climbing right turn. Finally observed helicopter Y hovering over the trees just off the landing pad over the approach path. [I] circled to the right on a normal pattern after wave-off to uneventful landing. It's hard to believe that helicopter Y and Control attempted to depart their aircraft from that pad into the approach corridor given my ETA bearing a trauma patient. Since I was in a position to observe the approach corridor and the landing area it's amazing to me that I still could not see the aircraft; but our aircraft are painted drab colors and apparently blended into the scenery around the hospital (low and slow). I incorrectly assumed that because of the TCAD alerts and time lapse and the fact that I could not locate that aircraft in my intended flight path that there was no danger to rolling in on final approach. I had hoped to receive feedback from helicopter Y on the common frequency when I announced my intentions but failing that; I incorrectly assumed that his silence meant they were clear. I'll proceed more cautiously in the future around this hospital as it doesn't seem they're used to operating at the tempo that I'd expect.