These were the best performing ASX 200 shares last week

The S&P/ASX 200 Index (ASX: XJO) was out of form last week and dropped lower. The benchmark index fell 0.6% to end the week at 6,715.4 points.

Fortunately, not all shares dropped lower with the market. Here's why these were the best performing ASX 200 shares last week:

Pro Medicus Limited (ASX: PME)

The Pro Medicus share price was the best performer on the ASX 200 last week with a massive gain of 17.1%. Investors were buying the health imaging software company's shares after it announced another major new contract win. Pro Medicus has signed a seven-year contract worth $40 million with Salt Lake City based Intermountain Healthcare. The deal will see its Visage 7 Viewer and Visage 7 Open Archive products implemented across all of Intermountain's radiology and subspecialty imaging departments. This is its fifth major contract win in the space of six months.

Afterpay Ltd (ASX: APT)

The Afterpay share price wasn't far behind with a 14.8% gain over the five days. Bullish sentiment in the buy now pay later sector following Affirm's IPO in the US and a positive broker note out of Morgan Stanley gave its shares a boost. In respect to the latter, Morgan Stanley retained its overweight rating and lifted its price target on the payments company's shares to $136.00. The broker points out that app downloads have been increasing strongly in the US and UK. It is expecting Afterpay to report 13.6 million active customers for the first half of FY 2021. This will be a 37.4% increase from 9.9 million active customers at the end of FY 2020.

Whitehaven Coal Ltd (ASX: WHC)

The Whitehaven Coal share price was on form last week and recorded a sizeable 13% gain. This followed the release of its quarterly update, which reaveled that Whitehaven Coal achieved a 64% increase in managed run-of-mine (ROM) production to 5.1Mt for the three months ended 31 December. And while its sales were flat on the prior corresponding period, management has tightened its sales guidance range to between 19Mt and 20Mt from 18.5Mt and 20Mt. The company also revealed that coal prices have been improving strongly.

Mesoblast limited (ASX: MSB)

The Mesoblast share price returned to form at last and jumped 9.4% over the five days. Investors were buying the biotech company's shares after it finally released a positive announcement. Mesoblast announced that its rexlemestrocel-L drug provides a reduction in heart attacks, strokes, and cardiac death in patients with chronic heart failure. According to the study, heart attacks and strokes were reduced by 60% from a single dose.