Importance Twitter has recently been explored as a data source by researchers in multiple fields, though, as a whole, the research remains nascent. Even less is known about using Twitter to study cardiovascular disease. Objective We sought to characterize the volume and content of tweets related to cardiovascular disease, and the characteristics of Twitter users. Design We used the Twitter Application Programming Interface (API) to access a random sample of tweets from July 2009 to February 2015. We filtered approximately 10 billion tweets for keywords related to cardiovascular disease. We included only English tweets originating from US counties. We characterized each tweet relative to estimated user demographics. A random subset of 2,500 tweets was hand-coded for tweet content and modifiers. Setting Twitter, a social media platform Participants Twitter users tweeting about cardiovascular disease Exposures None Main outcomes and measures Our main outcomes included the volume of tweets about cardiovascular disease on Twitter and the content of these tweets. Results Diabetes (n=239,989) and myocardial infarction (269,907) terms were used more frequently than heart failure (9,414) terms. Users tweeting about cardiovascular disease were more likely to be older than the average Twitter population (mean age= 28.68 vs. 25.36, p<0.01), and less likely to be male (47% vs. 49%, p <0.01). Most tweets (94%) were health related. Common themes included tweets related to risk factors (42%), awareness (23%) and management (23%). Conclusions and relevance Twitter offers promise to characterize public understanding and communication about heart disease.