A graduate of the Phoenix Ulster Academy, Heaney has represented Ulster at all levels and made his senior debut for the province in a pre-season friendly away to Harlequins in August 2010.
He was a member of the Ireland Under-20 squad that won the 2010 Six Nations title and also competed in the IRB Junior World Championship later that year.
The 21-year-old scrum joined Doncaster midway through the 2011/12 season after playing his club rugby in Ulster with Belfast Harlequins.
Sean Doyle is an Australian-born openside flanker who has joined from Sydney club side Southern Districts. The Irish-qualified 22-year-old has been one of the leading players in the New South Wales Premier Grade over the past four seasons and has also been a strong performer for the NSW 'A' representative side.
Meanwhile, former Munster and Aironi back rower Nick Williams will be playing his rugby with Ulster after penning a two-year contract.
Weighing 120kgs, Williams is an intimidating presence on the pitch and is regarded as one of the most explosive ball carriers in Europe.
The 28-year-old New Zealander had a successful career in his homeland, making 37 Super Rugby appearances for the Blues during a four-year spell. He also played for North Harbour under new Ulster head coach Mark Anscombe in the Air New Zealand Cup.
Williams joined Munster ahead of the 2008/09 campaign and helped them secure the Magners League title in his debut season. He then moved to Italian franchise Aironi and his scoring record of 10 tries in 31 league games underlined his importance to them.
Ulster director of rugby David Humphreys believes Williams will prove to be a major success in Belfast as his side targets success in the RaboDirect PRO12 and Heineken Cup.
"Nick was a standout player during his time at Aironi and he will add a great deal to our squad," explained Humphreys.
"His addition means there will be real depth right across the back row and this is vital, given that Stephen Ferris is under an IRFU player management programme.
"Mark Anscombe brought him out of club rugby in New Zealand and believes he can make a huge impact here at Ulster. He is an excellent ball carrier and is a very physical in defence."