To be assessed for eligibility (n = 6000) To be enrolled (n = 1200) To be analyzed ("tPA eligible") (n =693) Based on our pilot data in the first 9 months of operation, the MSU is being alerted and dispatched by Criteria 1 above approximately 5 times for every patient that is enrolled into the study by Criteria 2, and 10 times for every patient treated with tPA by Criteria 3. Therefore, we anticipate that slightly over 50% of enrolled patients will be treated with tPA. We calculate that we will need 693 tPA eligible patients (meeting above Criteria 1, 2 and 3) to answer SA 1 allowing for 10% lost to f/u (see Statistical Methods).