(as) serious as a heart attack

1. Completely sincere or earnest. Does it look like I'm laughing? I'm as serious as a heart attack. I'm prepared to sue if you don't stick to our deal. Oh, the mayor was serious as a heart attack in his plea. This area needs government aid to be able to address the sweeping electrical outages caused by the hurricane. I knew our teacher was serious as a heart attack when she threatened to give detention to anyone who disrupted class. Pete kept goofing off, though, so guess who has detention?

2. Very grave or alarming. This news about funding cuts sounds about as serious as a heart attack. If what I'm hearing is true, it could jeopardize our whole research project! The situation here is as serious as a heart attack. The hurricane has destroyed whole swaths of the town already, and it shows no signs of slowing down. Luckily, the residents knew the situation was serious as a heart attack and evacuated the building as soon as the fire alarm started going off.