The purpose of this Notice of Funding Opportunity (NOFO) is to solicit current or recently completed NHLBI K01, K08, K23, and K25 awardees for small grant support to expand their current research objectives or to branch out to a new study that resulted from the research conducted under the K award. Active NHLBI K01, K08, K23, and K25 awardees may apply for R03 support after the notices of award (NoA) for their first type-5 K awards have been issued. Recently completed NHLBI K01, K08, K23, and K25 awardees are eligible to apply for the R03 if the earliest possible R03 start date falls within 2 years of their prior NHLBI K award Project Period end date. This FOA is intended to enhance the capability of NHLBI K01, K08, K23, and K25 awardees to conduct research as they complete their transition to fully independent investigator status. This R03 grant mechanism is intended to support research projects that can be carried out and completed within a short period of time (no more than two years) with limited resources and that may generate preliminary data to support a subsequent R01-equivalent application. These studies include, but not limited to, pilot or feasibility studies; proof of concept studies; secondary analysis of existing data; small, self-contained research projects; development of new research methodologies or technologies, or development of novel experimental models. For current and previous K23 awardees, research proposed in the R03 application may or may not include patient-oriented research. A minimum of 40% protected overall research effort is required from applicants during the R03 award period and can be met through a combination of effort on the proposed R03 and other research projects, regardless of funding source.