not a heart attack like most think which is a coronary artery event in classic terms, flutter is an irregular heartbeat causing ineffective blood flow from insufficient filling and pumping causing syncope in some cases or passing out. Can happen to anyone without cardiac issues sometimes. Just bad that it happened while he was lifting.
anyway it must have been a significant sort of heart event, because getting 250 off your chest and onto the floor isnt too difficult, especially if you have a foot on the ground
unless it falls straight onto your neck, of course, but still..