1) self-reporting systems are subject to memetic effects. Like people calling in every suspicious thing they see to the cops if they hear the cops are investigating a high-profile murder, adverse effect reporting increases if people hear a rumor a vaccine may cause problems, whether or not anything in their day-to-day has actually changed.
2) The push to vaccinate everyone means a lot more people are candidates for reporting than in an average year. Given no side-effects from the vaccine, we would still expect VAERS reports to go up significantly. And since heart disease is a leading killer in the US, and unlike most vaccines, this vaccine is being given to the older population almost exclusively relative to the median age of most vaccine recipients, we're hard-pressed to distinguish "vaccine-caused heart disease" from "greater amounts of reporting from older patients resulting in more instances of heart disease showing up in the VAERS reports."