In this episode 60-year-old Margo, who has a lifelong heart condition which was first discovered when she was five, is in urgent need of life-saving surgery to fix a faulty heart valve. She must undergo a complex five-hour operation in which surgeon Chuck Maclean and his team have to stop Margo's heart before they can fix the problem.Donald, 78, needs an operation to implant a defibrillator to control a dangerous heart rhythm. But the procedure may have to be put on hold as he collapsed overnight, causing a head injury. He now needs a CT scan to find out if there's been any bleeding within his brain.Forty-seven-year-old Linda was born with Marfan syndrome, a rare condition that affects her heart. She has still managed to turn her passion for horse riding into a career, but her condition could trigger a life-threatening emergency at any moment.Geoff, 86, has had a fascinating career flying planes, but now he's at risk of heart failure. Open heart surgery is too risky for a man of his age, so Dr Angie Ghattas plans to repair his heart valve with a non-surgical procedure, inserting a tiny clip up an artery.