The 51-year-old sparked a massive police search after she went missing last month. Her body was found 11 days later in dense woods just a few hundred yards from her home.
More than 150 mourners gathered in Livingston, West Lothian, this afternoon to pay their final respects, with many having to stand during the service.
Her children, Andrea and Kevin Waddell, aged 24 and 27, wrote on the order of service: “To everyone else you’re Heather McKay, to us you will always be mum.
“Both Kevin and I will miss you more than you will ever know.
“You looked after us and taught us the ins and outs of who we are and we will never forget that.”
“You have taught me to be the person I want to be.”
They added: “I will carry you in me, you will live on forever in us. You really were one hell of a woman. My mum, my best friend.
“The love between and mother and daughter really does live on forever. Until we meet again I will think of you every minute of every day.
“I love you mum, I hope wherever you are, dad’s looking after you. If I can’t have you in my arms, I know he will look after you in his. Love you ANGEL. Sleep tight xxx”
A 1936 poem by American writer Mary Stevenson - Footprints in the Sand - was read during the service.
Mourners sang the hymn All Things Bright and Beautiful.
Heather went missing on the morning of Friday, August 24.
She had been staying in a house with friends in Dechmont, West Lothian, and her disappearance was said to be completely out of character.
It later emerged she had split with her partner, Gary Winters, before going missing, though the mother-of-two was said to be “bouncing back”.
Andrea made a tearful appeal for her return in front of the media on September 1 as fears for the 51-year-old grew.
A huge internet campaign saw thousands of people join the “Heather McKay Missing Person” Facebook group and volunteers comb the countryside for any trace of her.
But the family’s hopes were dealt a crushing blow when police announced they had discovered a body in woods near Dechmont on Tuesday, September 4.
The following day, the body was confirmed as being Heather’s. It was later revealed that she took her own life.