He 45a

First prototype, powered by a BMW VI 7,3Z piston engine.

He 45b

Second prototype, fitted with four-blade propeller.

He 45c

Third prototype, armed with one 7.92 mm forward-firing MG 17 machine gun, and one 7.92 mm MG 15 machine gun in the rear cockpit.

He 45A

Initial production version.

He 45A-1

Training version.

He 45A-2

Reconnaissance version.

He 45B

Improved production version.

He 45B-1

Reconnaissance version, armed with a 7.92 mm machine gun.

He 45B-2

Able to carry a 100 kg (220 lb) bombload.

He 45C

Production version of the He 45c.

He 45D

Slightly improved version. Similar to the He 45C.

HD 61a

Reconnaissance export version of He 45B intended for China, powered by a 492 kW (660 hp) BMW VI piston engine.

Sources:
Gunston, Bill - The Encyclodepia of the Worlds Combat aircraft, 1976, Chartwell Books, Inc., New York
Brown, Eric, Captain - Wings of the Luftwaffe, 1979, Airlife Publishing Ltd., Shrewsbury
Gunston, Bill & Wood, Tony - Hitler's Luftwaffe, 1977, Salamander Books Ltd., London
Donald, David - The Complete Encyclopedia Of World Aircraft, 1997, Brown Packaging Books Ltd., London
Wikipedia - Heinkel He 45