The authors took 17 adults and gave them their choice of a comedy video and a documentary and then measured a variety of markers of vascular health (brachial artery flow-mediated dilation, arterial compliance, etc.). They took measurements after each video for each subject and found that watching comedy improved the measurements, suggesting that laughter elicited by comic movies induces beneficial effects on vascular function.
Now, as a doctor, this trial means nothing in terms of how to provide patient care. Clearly I can't prescribe 2 hours of Seinfeld daily and expect that to prevent heart attacks. That said, perhaps I should watch Clerks instead of The Wrestler tonight.